It's not just because it's a jeep , it happens to all vehicle's . My chevy is doing the same thing right now and it been like that for about 1/12 years. It could be one of the rear wheel bearings or as simple as a bad tire that's causing the noise. They usually get real loud before they go out .
Hmm.....I used to own a 96 Grand Cherokee. The rear diff needed to be replaced. I'm not too knowledgeable on the specifics like you stated. But.......I would never own a Jeep again, that I can tell you. Bailout anyone?