Differential noise when gear is place. in reverse or drive.

limited info generic answer pinion not set -shimmed or torqued correct ---axle bearings --brakes -parking/regular ------gear not installed correctly ----fluid

Yes, differential.

I would guess your differential. Raise your rear end and try rotating wheel, it should make the other wheel spin the opposite direction. I'd the other wheel doesn't spin, I would say it's your differential.

the transfer case only engages when in 4wd. check the universal joint, it connects from the drive shaft to the rear differential. it may need grease or to be replaced.

Probably broke your U-Joints on your driveshaft, preventing the rear wheels from turning. Your driveshaft might have disengaged from your differential too. check underneath concentrating on the driveshaft and differential

if the diff is not leaking oil there should be no reason to be low. If you hear a noise in neutral with the truck not moving, its not in the rear end. it may be the trans or transfer case.

my 2003 silverado z71 rear end is stamped 8.8 on the axle is a 8.8 or a 8.5 ? 5.3l 3.73 gears g80 locker

This could be one of several problems: If the noise increases with speed, and you are only hearing it from the rear differential and not the transmission, it could be the rear differential carrier bearings, or rear axle bearings going bad. If you are only hearing the noise upon acceleration or deceleration, the rear differential ring and/or pinion gears may be going bad and the rear differential will need an overhaul. You'll have to get the rear wheels off the ground and see if you can pinpoint the location of the noise with something such as a stethoscope. If it's coming from the rear differential, you'll need to pull the bolts and the cover to determine if the gears are still in good shape, or if there is any pitting. Same with the carrier bearings; if you see pitting/ discoloration, they'll need replacement. If the noise is coming from one side towards the end of the axle shaft near the wheel, it's most likely a axle bearing going bad, and you'll need to pull the wheels, remove the diff. cover to release the C clip which holds the rear axle in place at the differential, and pull the axle out. You also need a special tool with a slide hammer to remove the axle bearing and seal.

I would suggest a rear differential service. When the fluid breaks down in the rear it doesn't provide the proper lubrication for the rear and you'll hear the "moan". Don't forget to buy and add the limited slip(posi-trac) additive.

As far as the rear end noise, There was a TSB released on GMC light duty trucks that says "Some owners of light duty trucks equipped with automatic transmissions may comment that the vehicle exhibits a clunk noise when ******* between Park and Drive, Park and Reverse, or Drive and Reverse... Whenever there are two or more gears interactin with one another, there must be a certain amount of clearance between those gears in order for the gears to operate properly. This clearance of freeplay (also known as lash) can translate into a clunk noise whenever the gear is loaded and unloaded quickly, or whenever the direction of rotation is reversed." It goes onto say "...Whilse some owners may find the clunk objectionable, this will not adversely affect durability or performance."

I believe that it is 80w90 but you also have to add differential additive for locker that is inside. you can purchase additive at chevy dealership, napa, or other parts stores just make sure it is formulated for gm.