In my last job, I had a new car with 3.5” jack input into the stereo. This was so I could plug in my PDA/Music player/GPS into the stereo. It worked great until I needed to put the phone on charge.

As I put my foot down, I would hear noise come out of the stereo, increasing as I accelerated harder. It wasn’t a terrible noise, but enough for me to ask others about it. It was very frustrating to me and I had no idea what could be causing it.

A colleague told me about Ground Loop Isolators which would fix the problem. I don’t really know how they work, but it grounded my device when on charge, and killed the noise entirely.

They are a little frustrating to use as you often need to convert from jack to RCA and back again in stereo, but with a few adaptors and somewhere to store all the cables, this is what you need. They are available from just a few dollars and up. The one I got was cheap, and did the job well.