Car Tech: Jeep Grand Cherokee Radio/Electrical Issues

Jeep Grand Cherokee Radio/Electrical Issues

I'll try to keep this brief: I have three major issues, one which is more important to me than the others.

The two issues of lesser importance are the intermittent operation of the power locks. Sometimes they'll work when I press the lock button on the driver's or passenger's control panel, sometimes they won't. The other lesser issue is that the interior lights stay on with the doors closed. I've checked all the switches on the door frames. I ended up having to pull the fuse so that my battery wasn't depleted.

The major issue I'm having is a nasty feedback through all four speakers. I've been assured that the speakers themselves are functional, and I replaced the radio hoping that would solve it, but no dice. Could it be electrical? I have no idea what to begin looking for. I just replaced the alternator (after being told I needed to replace the ECC and getting my hopes up that it would fix all my problems), and it was a HUGE hassle, so I'm rather exasperated at this point. Any help would be appreciated.