Unable to locate source of Audio Ground Loop / Noise
I have been troubling with this issue for the past 8 days and I have exhausted all my options.
I am using the factory amp / speakers.
The factory amp input cable has 4 audio channels and 1 common ground, so I made RCA cables with the center pin for each channel, and tied all the grounds together. When I hook up my iPod, there is no noise, and it sounds great. When I have it hooked up to my soundcard (external USB Sound Blaster Live 5.1), there is a very small amount of noise with the key off, but as soon as I turn the ignition on, there is all kinds of noise. It picks up throttle movement with the car off (throttle is drive-by-wire). It almost sounds like a microphone is plugged in and picking up all kinds of ambient noise. Against better judgment, I bought ground-loop-isolators for all the channels, and that didn't really seem to do anything.
My last option will be to buy an aftermarket amp that actually uses 4 independent channel grounds, instead of a common ground, like my factory amp. I just am at a loss for where this noise is coming from.