Hey, Mine was doing that at 104K miles, what it sounds like is planetary(spider) gears in the diff(carrier). When you pull the cover check the teeth on the little gears in the center of the diff. Also check for wear on the shaft(s). Randys ring & pinion sells a complete kit with instructions on their website..Not too tough a job, just stinky and oily messy. Hope that helps. | 
