87 Sub w/ Rear R-side Squeak at 5-15mph - break adjustment???

I have an 87 GMC Saburban that is squeaking on the right rear side. I thought it was in need of a break job but after pulling the drum off and checking it out the break pads are fine. At 5-15MPH it squeaks like crazy, but if I apply a small amount of pressure to the break it stops... thus my thinking that it's a break adjustment.

Any advice?? I can't seem to locate the adjustment to stop the squeaking, have not done a break job before, and can't seem to find anything on the net about it.

Please help - thanks!