I just integrated a 4ch amp for my new surrounds, and 2 channel amp for a sub to the stock head unit.
Before I added anything to the stock system, I noticed that when the radio was on AM stations, that I would pickup engine noise (it varied with RPM). Now that I have amps, the situation is horribly worse. There is constant engine noise whether or not the stereo is turned on, and it still varies with RPM.
I'm going to remount my sub amp so it is not directly on the cars metal. What concerns me is that I had an engine noise problem when the system was stock. I replaced my head unit with another factory unit (under warranty, sort of), so I know that's not the problem. Where should I start for that prob?