Yukon xl "coast down howl"

I've got a 2001 yukon xl 4wd with 22000 miles on it. When decelerating from 65 to 50 mph the rear end produces a high pitched howl. The dealer says it is normal, yet none of my friends who own yukons have the problem. Iam sure there is a problem. Any thoughts ?

Did you check and see if theres any oil in the diff ?
Sometimes a quiet howl is forgivable, but if its loud , its trouble.

I had the same problem but it was the carrier bearings in the front end.Local 4wd shop fixed. Cost me 448.00 but no noise at all now