I asked because the title of your first post said "Qudra Drive" and it wasn't clear (and still not clear) that you have Quadra-Drive. The NV247 could mean that you have Quadra-Trac II or Quadra-Drive. If QD, there should be a "Quadra-Drive" emblem on the transfer case bezel around the shift handle in the cabin. There should also be a "Quadra-Drive" emblem on the lift gate. The difference between QTII and QD is that QTII has open differentials while QD comes with Vari-Loc (a type of limited slip) differentials at the front and rear.
Your sounds could originate in the NV247 and travel to the rear end with either QTII or QD. Since your WJ came from a used car dealer, I would guess that the lube in your NV247 is an ATF of some type. That works for a while, but sooner or later clutch chatter will occur in the NV247. The correct lube is Mopar NV247 transfer case lube found only at a dealership. I suggest that you replace the lube with Mopar lube. Even after that is done, it will probably take a while for the NV247 lube to work its way into the clutch pack so the sounds might not go away immediately.
If you have QD, it's important to know that the differentials need a friction modifier added to the gear lube. Without the FM, clutch chatter is guaranteed to occur. Since you don't know much about the history of your WJ, it wouldn't hurt to go ahead add 4 oz of FM to the rear differential if changing the TC lube doesn't help. You will probably have to remove some of the original lube in order to make room for the FM. As with the TC, it may take a while for the FM to work its way into the clutch pack and quiet things down.
If you have QTII, and if changing the TC lube doesn't help, then there is probably a problem with the rear end.