Well, just to close the loop on this thread, I found the problem. Removed sub woofer amp and took it apart. One of the connector pins for the connection to the truck harness was internally broken and not physically connected to the circuit board inside the amp. So rather than try to source and install a whole new connector on the circuit board, I simply soldered in a jumper wire to jump the bad pin and then soldered it to the harness in the truck. The amp now works properly and I have no more buzz. Once connected I realized that the amp wasn't even working prior to this, and probably hasn't ever worked, as it looked like it was this way from the factory.
Oh, and by the way, I have also successfully disassembled, troubleshot and rebuilt the 6 disc CD changer mechanism that was previously jammed as well as fixed the dim display issue, so if anyone wants theirs fixed, I can do that for you.