Noise suppression guide

Diagnosing and treating noise problems in your car audio system


Buck Pomerantz

Buck Pomerantz was born and raised in Philadelphia. His parents bought their first television set when he was born. He figured out how to run it by the time he was two. Besides athletics, his formative interests included electronics, amateur radio, music, and stage crew work. He got his BA in writing from Brown University. Then he joined a rock 'n roll band as their soundman and moved to Charlottesville, Virginia. After that venture failed, he spent time in Boston, New Orleans, and Berkeley. He worked in a music store in Austin manufacturing, installing, repairing, and operating sound systems for recording studios, clubs, and bands. He moved back to Charlottesville, ran a little recording studio and finally joined Crutchfield as a copywriter. He has 2 grown children and 3 grandchildren, but after a good nap he can still rock out.

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Noise Suppression Guide
This guide will help you diagnose and treat problems with extraneous noise in your car audio system. You can also download a PDF of the Noise Suppression Guide. (hide this initially, until the PDF is updated)

Dealing with noise

You've installed a new receiver or amplifier in your car, and now you have a noise problem. What can you do? The trick is to determine what the source of the noise is. Noise can be introduced into your system from a number of sources. This is especially true if you have an amplifier. The type of noise you're hearing can help determine the cause.

Read over this article for some hints and explanations of what can cause noise in your system. Use it as a checklist, eliminating possibilities until you find the culprit. You can also use this diagnostic flowchart as a guide to walk you through the troubleshooting process.

And don’t forget – if you purchased your gear from Crutchfield, or purchased tech support separately, don't hesitate to call on our tech support team (have your Crutchfield invoice handy).

Noise and your new receiver

If you’ve just installed a new receiver, here are two quick and easy starting points:

Receiver with antenna lead, power, and ground

Noise in your receiver is often due to a poor ground wire connection or a poorly grounded antenna.

Is your receiver securely grounded?

Improper ground is one of the biggest causes for introducing noise into your audio system. Is the ground wire located near a noise source (like a heater, air conditioner, or computer)? Is the ground wire actually connected to the vehicle's ground? Since the antenna lead can act as a ground (thereby enabling a new receiver to operate without its ground wire properly connected), the antenna lead is frequently the source of noise problems.

Antenna noise

Check to see if you're getting noise on all sources — CD, auxiliary/USB, AM, and FM
If the noise is present only on the radio, then it's most likely coming through your antenna lead.

Unplug the antenna. If the noise goes away, try an antenna noise suppressor (like American International's AS100). This filter plugs in-line between your receiver and your antenna, breaking the ground path between them, thus preventing noise from entering your system.

Antenna filter

An antenna filter, installed between the vehicle's antenna and the receiver, can minimize noise entering your system from a poorly grounded antenna.

Radiated noise

If the noise isn’t coming in through the antenna, try pulling the receiver from the dash while a CD is playing. If the noise goes away, it's being radiated into your system due to the receiver's proximity to a noise producer (like a heater motor or car computer). This is often referred to as “sideway noise.”

If the noise-causing accessory has a motor, a source noise filter can be installed on the accessory's power lead to minimize radiated noise. If the car computer (or other motor-less accessory) is causing the problem, move your receiver's wiring away from that accessory to minimize the radiated noise.

Try using magnetic shielding foil (also called Mu-metal) to shield the back of the receiver or wrap the wire or component that's radiating the noise into your system.

Engine noise

Noise introduced through the power and ground wires connected to your receiver is called engine noise (sometimes referred to as “backway noise”). If engine noise is your culprit, you may hear a whining or clicking sound. Its pitch will usually vary with engine speed.

If this is the case, you can install an alternator noise filter on the power line between the battery and the alternator to minimize the problem. You can also install a noise filter on the receiver's power lead to cut down on signal pollution (American International's S15A (15-amp, 250-watt) or S25A (25-amp, 350-watt) filters, for example). Most often, however, backway noise comes from a loose or intermittent ground connection. See the section below about noise in the electrical system.

Alternator noise filter

An alternator noise suppressor connects inline between the alternator and battery, and can reduce high-pitched whining noise that modulates according to engine RPMs.

Noise and your new amplifier

An amplifier can introduce noise into your system through a bad ground or through a poor mounting. Rubber grommets or feet can help isolate the amplifier from the chassis of the vehicle, a potential source of noise. If all else fails, install a noise suppressor. The tricky part is figuring out which step or steps to take. Please read the rest of this section and try some of the simple tests.

Amplifier connections

Where is the amp mounted?

Is it near something that could be radiating noise, like a rear-mounted tuner or computer? If so, unbolt it and move it away to see if the noise stops. Remove your patch cables. If you still hear noise, check to see if your amp is isolated from the vehicle's chassis. Any contact between your amp's metal casing and your vehicle's body could cause noise problems.

Check your ground wire

Is it securely attached to the vehicle's chassis with a good contact to clean metal? Your ground wire should ideally be 18" long at most — a longer ground wire can cause noise problems. Improper grounding causes most system noise problems.

Check your gain structure

If you have an external amplifier in your system, the first thing to do is to quiet any system noise, which sounds like a constant, low hiss. First, check for system noise with the engine off. Insert a CD and put your CD player on pause. Listen to the system with the volume way down, then way up. Put on music. If you hear hiss in either instance, reduce the gain on your amplifier.

Pass more signal from the receiver to the amp by leaving the receiver's volume higher before you set the amp's gain. Experiment until you eliminate the hiss or reduce it as much as possible. A tiny bit of hiss is OK — you won't hear it while driving.

Noise in the patch cables

Noise can be picked up by the RCA patch cables connecting your components. To test this, detach the cables from your amp. Insert one side (left or right) of a spare patch cable into the amp's left and right input jacks (see illustration below). Turn on your system and engine.

RCA noise

If the noise is gone, reconnect the cables to the amp, and disconnect them from your receiver. If you hear the noise, your patch cables are definitely picking it up. Try re-routing them. Separate them from your power cable by at least 18 inches. You could try a better brand of patch cables. The inexpensive RCA cables many people use to connect their components don't have the insulation or conductivity necessary to deflect noise in a metallic, highly conductive automobile.

How much noise your cable receives depends largely on the size of its “loop area;” the larger the loop area, the more vulnerable your cable is to induced interference. A cable's loop area is equal to the distance between its center conductor and outer shield times the length of one complete twist in a twisted pair configuration, or the entire length of the cable in a coaxial type. Consider trading your old cable for one with a twisted pair design. You'll get a smaller loop area and less noise.

Twisted pair patch cables

Patch cables with a "twisted pair" design help reject noise

As a last resort, a ground loop isolator (like PAC's SNI-1) can be installed between the receiver's preamp outputs and your amp to minimize this problem.

Noise picked up by the power or ground cables

We discussed ground cables above, because that’s the cause of noise more often than not. If the noise wasn’t due to a poor ground or through the stereo’s antenna cable, it may be coming in through the amplifier's main power cable. Noise can be created by cable of insufficient gauge, so you might try thicker cable.

Ground loop isolator

If you cannot find the faulty ground in your multi-amp system, a ground loop isolator can help minimize the problem.

Multiple amplifiers can also create ground loop problems, which can usually be solved by grounding each amplifier with its own separate wire. If you are unable to locate the cause, a ground loop isolator (like PAC's SNI-1) can be installed between the receiver's preamp outputs and the amplifiers to minimize this problem.

Noise in speaker wiring

Noise can also come in through the speaker wires. To test them, turn the system off and disconnect the speaker wires from the amps. Now start the car. If the noise is still there, then it's being radiated into the speaker wires. Reposition them, or, as a last resort, shield them by wrapping them with Mu-metal foil.

Noise from electrical system

If you've tried all of the noise-fighting tips above and you still hear the noise, the problem might be with your vehicle. You might simply need to fill your battery with fluid. If that doesn't help, have a mechanic check your alternator and battery.

If your car is older and hasn't been tuned up recently, you may have ignition noise. It's a ticking noise that varies in speed as you accelerate. You may need a tune-up involving resistor-type spark plugs, shielded carbon-core spark plug wires, distributor cap, and coil.

If the noise doesn't disappear, then your ignition system may not be grounded well enough and is broadcasting ticks to other items such as your air cleaner, hood, exhaust system, etc. Chances are, grounding one of the under-hood components will eliminate the noise. With your sound system on and the car running, try grounding each of these different components of the car. It's possible that grounding one of your car's components will eliminate the noise. If so, make the ground permanent with a braided ground strap.

A very effective fix for electrical system noise is called "The Big Three" upgrade. This is where your vehicle's battery charging wire and chassis ground wires are augmented by adding large gauge wires (1/0- or 4-ga.) to those connecting the alternator to the battery's positive pole, the battery's negative pole to the chassis, and the chassis to the engine block. This establishes better current flow and more consistent voltage, which improves your system's signal to noise ratio. It also ensures against loose or restrictive ground connections, which, as said before, are common sources of noise. Read our article about The Big Three for more information.

Noise and your nervous system

Noise problems can be very frustrating, especially when you can't wait to hear your new equipment. It helps to remember that you've just placed a very sophisticated piece of electronic gear (a new receiver or amplifier) in the middle of an extremely complex system — your vehicle's electrical wiring. Noise is just nature's way of telling you that something's out of whack. Just run down the list, eliminating possible noise sources until you find the problem.

Crutchfield Tech Support

If you bought your gear from Crutchfield, you could call Tech Support for free help troubleshooting your system. The toll-free number is on your invoice. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support — 90 days-worth for only $30.

  • Loren from United States

    Posted on 7/12/2015 10:47:48 PM

    I need a filter! I am running my karoke (on my computer) using head phone jack and going to my amp?speaker.. it is a guitar amp. But I am getting "computer noise" through the amp is their a filter available to stop the noise?

  • Buck Pomerantz from Crutchfield

    Posted on 7/14/2015 11:52:30 AM

    Loren, I'm not sure what "computer noise" means, but using the headphone output of your computer to feed a guitar amp's input has probably set up a ground loop which hums or buzzes. Guitar amps by themselves are inherently noisy. Have you tried plugging the amp into the same power strip as the computer? Have you tried switching the amp's ground lift? Sorry, Crutchfield doesn't carry an isolation filter for this situation.

  • Daniel from Muncy

    Posted on 8/12/2015 4:16:42 PM

    I'm trying to hook a car amp and subwoofer to my home theater system using a ac to DC power converter. When I hook everything up correctly I turn on my home system. When I play country music on the home system I'm getting an entirely different channel playing music through the car amp and subwoofer only. Country on the home system and classic rock on the amp and subwoofer only. Any reason why this is happening?

  • Buck Pomerantz from Crutchfield

    Posted on 8/13/2015 12:15:51 PM

    Daniel, It sounds like your subwoofer amplifier is plugged into a tape output that's tuned to a different source than the main output. Like you're playing a CD while the tape out is set to the FM tuner. Normally in a home theater system a subwoofer gets its input from the receiver's LFE (low-frequency effects) output, which plays the bass of the program playing.

  • mike from roseville

    Posted on 8/30/2015 4:40:12 PM

    I am having popping noises comming from the speakers when I turn my system off. I have a jl audio v2/75x4 watt 4 channel amplifier and a pioneer deh-x8700bh head unit along with alpine spr-60c and spr-682. thank you for your time

  • Buck Pomerantz from Crutchfield

    Posted on 8/31/2015 12:25:35 PM

    Mike, Usually those kinds of noises are the results of a loose power or ground wire. Check that first. If you bought gear at Crutchfield, you could call Tech Support for free help troubleshooting your system. Their toll-free number is on your invoice. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support - 90 days-worth for only $30. Click on this link for details.

  • Chris from Baltimore

    Posted on 9/30/2015 11:15:15 PM

    Hello Buck. I was thinking about installing a home/computer speaker system I already have into my car in order to save money. The speaker system I have is the Klipsch Promedia 2.1 at 200 watts total system power (2 speakers and a 6.5inch subwoofer). It has an amp with a subwoofer knob and a main volume knob. The amp is described as a "Digital/Linear A/B Amplifier". The 2 speakers connect to the back of the sub, as does the amplifier, and the system power cord. -To my understanding, all I will need to buy in order to install these in my vehicle is a power inverter? Would a 1000W power inverter be enough? -The power cord coming out of the sub (that powers the whole system) only has two prongs, as in there's no ground. This would plug into the inverter which would be wired straight to the battery. Do you see any potential problems here, either with grounding or possible noise? I guess I won't know until I have the system installed but if it won't work, I'd like to know before I buy the inverter. Will I need an isolation transformer between the inverter and the speaker system or a ground fault circuit interrupter, or a ground loop isolator? Thank you.

  • Buck Pomerantz from Crutchfield

    Posted on 10/1/2015 10:30:36 AM

    Chris, I do not recommend putting stereo gear designed for home use in cars, where road noise and listener positioning become obstacles to fidelity. What you propose is possible, but it won't be as loud as you think. Klipsch rates that system as 35 watts per speaker and 50 watts for the sub (120 watts total) while playing at 5% THD, audibly distorting. A more realistic interpretation would be to expect about a clean 70-watt total output. AB amplifiers are about 50% efficient, so a 150-watt inverter should work. Don't forget to firmly secure the gear in your car so that in the event of an accident pieces of equipment don't become lethal projectiles. As far as noise issues, you can't troubleshoot a problem that doesn't exist yet, but equipment designed for home use may not work very well with a car's electrical system.

  • Joel cawoski

    Posted on 10/28/2015 9:44:36 PM

    I am having a problem with my amplifier/ car speakers. The system sounds great with the key in the accessory position. When I turn the key the full way to start the ignition there is buzzing sound. The buzzing sound is constant at any volume even on zero. The rca cables are routed on the opposite side of the power cables so it can't be that. How do I fix this problem?

  • Buck Pomerantz from Crutchfield

    Posted on 10/29/2015 12:40:47 PM

    Joel, Locating and correcting noise issues in a car audio system are often difficult and confusing. Most of the time noise is caused by a loose ground connection somewhere. As an aid, we've made an interactive flow-chart, that you follow step-by-step, in order to help you solve some common noise problems. Go to How to diagnose and suppress noise to start your troubleshooting.

  • Josh from Champaign, IL

    Posted on 11/23/2015 4:39:51 PM

    I finally located the source of my whine/squeal/ringing. I replaced my head unit thinking that was the problem. That didn't do it and it does it whether the engine is on or off. Finally sat and listened, realized it was coming from the rear. Got in the trunk and figured out that it was a faulty mini-sub from the factor. Unplugged it, problem solved! 2002 Nissan Sentra.

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