my wife's 2001 Explorer Sport is making a clicking noise i believe from the rearend that clicks at the reveloution of the tire. it only makes the noise in motion and increases with speed. I first took apart the disc/drum setup (it is disc brakes with a drum parking brake inside the disc) in the back thinking it might be a broken and dragging spring because she has a parking brake light that hasnt turned off in months.. the pass side drum was really hard to get off it drug a little but after loostening both sides up a little it still makes the noise. the u-joint in the driveshaft seems to be in good condition. I dont really want to pull the diff cover unless it could really be a possible ring-gear. it doesnt sound like one to me atleast.

any ideas?