bent housing?
I think my old housing was bent and I broke 2 diffs the exact same way.
the left side bearing race retainer on the diffs sheared off.
Rear was quiet for about 10K miles and then it started to whine under load and then I sheared almost all the teeth on the ring gear off.
If you have a manual, I would take it easy on that rear.
pic of the carnage,

