i had my alpine deck installed, and because i just bypass the amp without using the after market one, there is a ground problem..
and my car now sounds like a R/C car also...it's more like a high pitch sound you hear in the WRC cars !!lol!!
i personally think it sounded cool so i ignoreed it
I have a similar thing going on too, it was something to do with the harness or something and at low volumes when I am I drive or have the engine on that it makes this high pitch sound.. which can be solved by merely turning up the stereo or turning it right off.. sucks because I paid like around $300 just to have the thing installed and I end up with that problem.