have a 90 LS and replaced my old factory pioneer headunit since it went kaput a few months ago. it would not power on sometimes and gradually got worse, finally it just stopped working. i tested the power harness going into the headunit and it checked out okay. i got a replacement factory pioneer headunit, this time with the cd changer button, so i can go ahead with wiring in an ipod into the cd inputs after i find a cheap m-bus pioneer changer to wire in.

i noticed that i'm getting terrible feedback noise and the pitch is proportional to the engine rpms. it sounds like i can hear the alternator whine through the speakers and it's only audible when the volume is set low enough that the music level doesnt cover up the noise.

where should i check for a bad ground connection?