I have a whine, not sure if it's transmission or transfer case or what. It makes it when decellerating and badly in reverse. It gets worse as a downshift decelerating, like in 4th I rarely hear it... 3rd I hear it sometimes, and 2nd just about always whines (don't use 1st of course). And when backing out of a space in reverse in really whines bad. I changed the transmission gear oil twice and changed the transfer case fluid (ATF) when I first got the truck 8K miles ago. I know it's very hard to decribe this noise, but whine is the best way I can think of. My bro said possibly the mainshaft in the transmission, just wanted to know otherss opinions also.