Okay, I've seen the suggestions on how to solve the problem. My question is this: If I take the ground wire from the radio and ground it directly to the firewall in my 2003 F-150 SuperCab, where is the best location to do this to keep the wire short?

I know that the shorter the wire is, the better.

I've had this problem since the day I installed my Kenwood DDX-7015. It didn't go away when I added my amps, nor when I took it back to the stereo shop and they added a "Heavy ground" wire (WTF that means, I don't know). I grounded the casing of the radio to the factory ground along with the ground wire for the radio to no avail. Please help me eliminate this whine once and for all.... please?!