It could be either the transfer case, transmission, or a crank problem. Any failures with any of those systems could result in a banging or thumping system. There is also the possibility it could be the rear struts but that would be more of a banging when you go over bumps.

I have had the problem 3 times and fixed it 3 times over a 130,000 mile period. Cost to fix- Almost nothing.
The front end of the driveshaft has a sliding spline into the transmission. This spline goes dry and needs to be greased manually.
Raise the rear end and make enough room to get under the car. Using a 12mm open end wrench, remove the bolts in the rear universal joint(keeping track of where they go back in, using chalk) and remove the driveshaft.
On the front end of the shaft, clean the hollow end of the spline, and put several fingers-full of grease down in it, and make sure it is good and greasy. Reassemble the shaft into the transmission and reconnect the rear u-joint and the job is done.
Mine reoccurred in 25,000 miles, so I greased it again.
Permanent fix is to spend a couple hundred on a nickel plated yoke for the front end of the shaft. I prefer greasing the original one.