could be a couple of things, wheel bearing,pinion bearing or a differential bearing. if you can get a sthoscope and jack stands and jack it up safely and run the vehicle up to speed with a buddies help and place scope near each part, careful dont touch spinning parts.
hope this helps
1995 Grand Cherokee, 4" Rough Country,4.0L. HP30,Turdy 35 4.10 gears 33" Falken Wildpeak AT