Sounds like an axle bearing to me.
Take the rear shaft out and drive it on the front. If the noise is still there it is in the rear end.
You could also spin the rear up and put a long screwdriver on the axle housing and listen to the handle. If you here a grumbling in the handle it is the bearings.
Put all 4 on the ground. With rear ds removed. Locked it in to 4 wheel and took off. Lots of fun as my front is locked up. Made for an exciting ride. Still had noise. Got to the top of a steep hill. Disengaged from 4 wheel drive. Coasted down up to speed no noise. I think this eliminates rear ds, diff, and rear bearings. I think it is in either the transf case, intermediate diff or trans.. Any suggestions as to how to narrow it farther. Thanks.
