I don't know if anyone else has run across this, but make sure that the noise is coming from the rear end and not your 4wd hi/lo stick shifter. Any time that I decelerate, or if I'm just cruising along at a constant speed I get a "gear" noise that comes through the shifter. I have an aftermarket knob on the stick shift so that may amplify some of the noise. While it's happening, if I push on the shifter a little the noise goes away. It's done that since I bought it, and I've had all the fluids replaced to the correct level with Amsoil so I know it's all clean and full.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless