Agreed! Great input x91j and jjjingle36!
I have had the same problem for at least 3 to 4 years with the "growling" sound only on tight U-turns or parking lot manuevers. Going straight = no noise. Slow tight turns = loud growling sound from the rear differential. (At first I thought it was the front end.) We added the Jeep recommended limited slip differential lube (4oz.) to the rear end differential and the noise went away, no immediately but after about a week of driving. This was amazing as we have been putting up with that aggravating noise for a very long time. The vehicle is a 2001 Jeep Grand Cherokee with QuadraTrack (4 wheel drive all the time). Many thanks to you folks and this web site. I hope my confirmation of this similar situation also helps others.