Alt. whine caused by amp cover?

I've just been looking to narrow down the cause of my alternator whine in my newly installed system - I had the whine in my 206 scrap metal too, but never found a definite cause.

This morning though, I've noticed by accident that there are no problems when I run the amp without it's metal cover on (It's a cheap Fli900s 4ch.). Gave it some revs and no whine. I then screw the cover back on and it starts up again. I thought at first it might be touching the metal connectors of the RCA leads, but it's not. It's not touching anything it shouldn't, and just screws to the amp body as normal.

Has anyone got any thoughts as to why this might be the cause?



Sounds like a ground fault somewhere. Perhaps there's a dry join somewhere that's more apparent with the case on?