Nice find Cheese. Those are the hard ones to troubleshoot.
I also have a problem, I had a amp that went out and while I was waiting to get another one my buddy let me use his. It worked great, then when I bought a cheapy amp and put it in, it has a very bad engine whine to it. My question is, Do better quality amps have noise filters already internally? My amp that went out worked good as well with no engine noise.