Re-Ground HU or Ground Loop Isolator?
Ok, I've had my system in for nearly a year and am finally taking the time to try and reduce the noise. I'm running the PC with an aftermarket amp and stock head unit in a Chevy Avalanche. I've rewired the power and ground for the amp (the guy who originally installed it must have not been thinking correctly since the power wires were running right next to the signal wires) so that the PC and Amp share common power and ground.
I was getting some horrible alternator whine when using the PC, but I've added a ground loop isolator between the PC and the stock head unit and the noise from the PC is totally gone. The problem is that now I'm getting alternator whine from the speakers (much softer now) even with the head unit off. It's not dependent on the volume control of the head unit and when I unplug the speaker level inputs from the amp the whine goes away. That leads me to assume I've got a ground loop between the head unit and amp.
My question is this: Do I need to try to re-ground the head unit to the same location as the amp to try to eliminate the ground loop? I'm wary of this because of the long ground cable I would need to go to the back of the car. Or, do I get a speaker-level to RCA low-level converter and add a second ground loop isolator? With this, I'm worried about a second isolator somehow reducing my sound quality.
At highway speed I can't hear the whine at all and the sound is great, but with the stereo off or at low speed, it's annoying.