Hi,
it could be the disc is slightly warped and is binding on the pads each time around. It could also be a diff carrier bearing, the big ones on each side, that is wearing out or has gunk in it.
When looking for problems in the driveline make sure you stop one side of the diff from turning, or put it in gear if you want to test both sides, as the design of a diff means the energy will travel the path of least resistance so what you may think is on one side is actually the wheel on the other side or inside the gearbox binding or dragging.
Terry