I have a 2007 Pontiac Vibe that I bought used last year. The car had an aftermarket head unit and used the existing amp and speakers. There was no alternator whine. I installed a new head unit. That is the only thing I changed. There is now an audible alternator whine. I assume it is a ground loop. I've tested my HU ground and it looks good. I also tried grounding the HU directly to the battery. The whine continued.
I have yet to find any information about this problem when the stock amp and speakers are used. Everything discusses RCA cables, which I don't have. Could it still be the ground for the amp even though I haven't done anything to it and it wasn't there before?
I've played with all of the connections from the HU to the wiring harness. Nothing seems to make it go away. I don't know what else to do about the ground loop if my ground seems to be good.
I have read lots of proposed solutions but most don't seem to relate to my situation and those that do haven't solved the problem. Could there be a problem with the ground inside of the head unit itself?
Edit: Just to be clear, I've read tons of posts here and watched tons of videos elsewhere. I know there are a lot out there.