It probably is. I have an 09 that sounded just like you describe. If you grab the front of the prop shaft and move it there should be some movement from the factory about 1/16 should be OK. Anything more and something has came apart. Check the fluid to see if there is any trash, metal or plastic, (if you still have the plastic bearing carrier). Also look around the seal at the pinion to see if you have any fluid loss. Its normally one of the two, the pinion bearing failed, or the bearing carrier seal failed.
The sound carriers down the prop shaft tunnel and is also carried through the prop shaft it self. That is why it sounds like its coming from the rear. Just a FYI, if you do have to pull the diff I would recommend pulling the prop shaft and replacing the universal joints or you could be doing this again soon. The slop in the universal is a major contributor to the failure of the pinion bearing seal.
If you can, go with a 2011 or newer diff, which already has the aluminum bearing carrier and the pinion output seal area is completely redesigned, you will be much better off.
Good luck.
