whining sound when slowing down in my 07 Tahoe 4x4
 

So I've been having this whining sound when slowing down to a stop, its relative to my speed. Been doing research and possible causes are low diff. fluid/no diff. fluid. If this was the case, would i be able to switch from 2high to any other setting? This is the case with me, I can still switch from 2 high to auto to 4 high, did not try 4 low. Any suggestions, im not very saavy with checking the fluid levels myself. Most likely bring it to the dealer.

If no signs of leakage, doubt it's low fluid in diffs or transfer case. Does it do it if you slip into neutral while slowing down?

I did not try that, but I will tomorrow. What if it does not make the whine while in neutral, what do you suspect it means? Thanks for the advice!

UPDATE: Shark, I tried it this morning and no change in the noise whatsoever. Guess its time for the dealer, AGAIN!