Your best move at this time is to remove the rear cover and clean out the oil and any debris that you may find. As I remember the later Dana 60s use the TracLok (sp?) carrier (the weakest of the OEM models, single casting with big windows) and it has small parts that can break and become caught up in the ring & pinion. Open it up, clean & inspect with a fresh oil fill will cost less than $20.00 and at least you will know where you stand. Do it now!!