not sure if this is the right section but im having a problem with engine whine thru my speakers. i have stock mach system with a kenwood deck. for the last 5 or so months ive been getting that annoying whine, it went away for a months but now its back. ive checked the obvious and have relocated the deck ground wire 3 times now but no change. but here is the kicker, it only does it when im idling. as soon as i get to 1.5 g rpms it goes away. but as soon as i come to a red light or stop it comes back. it whines for a bit, goes away for a few seconds and comes back, so the sound is sporadic and not constant all the time while other days it may be constant and when i start the car it takes about 30 sec to make the sound sometimes, other times it may take 5 min.
ive even tried 2 different decks to see if it was my crappy kenwood. no change.
my next guess would be the alt but figured id ask here before i paid money to have it checked out.

 

Was going to say the ground.Usually a good chassis ground will cure the issue.But since you've done this,i'm not sure what it could be.