PAC SNI-1/3.5 Noise Filter
Crutchfield Customer Review (What's this?)
My iPhone, when connected to my car's aux input 3.5mm jack, was exhibiting loud buzzing when charging along with my car charger. I was skeptical of this device, since it doesn't have a third connection for a grounding cable. However, it reduced the buzzing to almost zero. I'm glad I took the risk with this device and it returned my car to clean-sounding-audio.