[Bigdav160]

Is it a high pitch like a whine (pinion bearings) or more like a growl (axle or case bearings)?

If you take the cover off, with a prybar, try to force the differential case (carrier to some) left and right. There should be no play.

You might have to pull the axles to check the axle bearings. Sometimes a mechanic stethoscope can be helpful but the axle tubes will transmit sound down to each end.