03 Sierra Rear axle loud clunking when turning

i would remove rear cover plate to axle ( pig ) and check for ring and pinion gear or spider gears for broken teeth. Or are you sure it's not a posi gone bad ? i would think that you have a problem with the pinion gear and or ring gear.

Suspect a worn left side spider gear or it's bearing in the differential. If a limited-slip differential, the left side clutch may be grabbing somewhat. In any case, the differential will need to be removed from the case to service any worn or defective components. Rear end service is not for inexperienced mechanics. Have you checked the fluid level in the differential? Hope this helps!

Sounds like your rear diff is winding up. possibly rear diff /or transfer box fault .

remove rear cover from rear differential. catch nasty smelling oil (gear lube) in drain pan. remove bolt on side of carrier to be able to pull pin out from so called spider gears. if you have limited slip you may hve to pull S spring out from between side gears. then push axles in and remove C clips fom end of axles. then pull axles out. installation is in reverse of removal. make sure that the C clips are well installed in the groves whe reinstalling axles, or they could fall out and axles will come out while driving. bad deal.if you have limited slip get a bottle of friction modifier from parts store to put in there with new gear lube . is a small bottle like 6 to 8 oz.kepps clutch packs from chatering on turns.

U MUST EMOVE THE CENTER PIN BETWEEN THE SPIDER GEARS OF THE GEAR CARRIER, THEN PUSH THE AXLE IN AND REMOVE THE "C" CLIP THAT HOLDS IT INSIDE THE GEAR CARRIER

Remove...
wheels, drums or rotors, the cover for the differential (You will need a drip pan)
remove the "pin" (usually a 5/15" or 8mm head) that secures the spider gear pin. Remove the long spider gear pin, as it should slide out without a lot of force.
Push both axles inward, and remove the left and right "c" clips that hold the axles in.
Note... if you have a limited slip, it may be a little different of a set up due to clutches in the differential.

Not that difficult, raise and support the rear of the truck and remove the wheels. Might as well replace both sides so you know you have new seals, remove the differential cover and drain the fluid. Once differential is opened and cleaned , remove the axle "C" clip that hold the axle in place and slide the axle out. Once the axle is out remove the wheel seal and clean around the area. This would be a good time to replace the wheel bearing too since you have access to them and there not that expensive. Install the new bearing and seal, note make sure you oiled the bearing and seal before installing it back and take care when installing the axle back in and "C: clip. Use RTV silicon gasket maker to seal the differential cover and wheels back on and lower. If your lazy like i am, you can drain the differential fluid and replace it with a 50/50 mix with gear oil and Lucas engine oil additives. That may stop the leak and get you a few more miles. You gear oil is 75W-90 and the capacity is 2.6 liters and 3.6 liters if you have the 11.50 Ring gear. Good luck and hope this helps. 

418238
If you have that much play back there, first check rear universal . If play is present in pinion with shaft removed, you will not be happy with what you find inside the cover.1/2 turn of lash in any gearset is far beyond the scope of any adjustment. Rebuilding is an exact science and must be done with special tools and lots of experience.
With any luck the u joint is bad...

do you know if you have a limited slip rear diff?
if you do your grease is worn out or if the fluid was replaced it need to have a friction modifier put in the diff (can be found at any auto part stores.)

if its not a limited slip diff you might have spider gears going bad. then you need to remove the cover on the diff and inspect your spider gears and these are the spider gears
and this is what a limited slip looks like
good luck
and dont forget to rate my answer
thanks
paul

There's a few more things to check out:
1. The track bar links, which attach from frame to the sway bar. Inspect the bolts/nuts to ensure they are really tight and the rubber isn't worn to the point of slack.
2. The bushings where the upper control arm attach to the frame. Inspect these for torn rubber/missing bolts. (These 2 bushings are on the fore end of the wishbone where you changed the upper ball joint.)
3. The bushings in the other, straight control arms that restrain the differential.
4. The shock absorber bolts/rubbers at frame and axle.
5. The u-joints on drive shaft.
6. The differential input pinion bearings. Raise vehicle and really yank/pry/push around the drive shaft and look for any slack.
7. The drive shaft at transmission. Check for any play over 0.020", side to side, up and down.
8. The transmission rubber mount.
9. The axle bearings. To check these, lift under axle, each wheel, and yank wheel fore/aft, up/down, and maybe use a pry bar. You're looking for axle bearing wear where the axle is supported at the outer ends of the axle tubes, just behind the brake mountings.
10. While the vehicle is raised (wheels off ground), chock the front wheels, and put transmission in neutral. Now check for significant slack when you manually rotate the wheels by hand, back and forth. If slack here (say, 10-15 degrees of fore/aft rotation on a wheel), then the spider gears are probably worn at the cross shaft in the differential carrier. Depending on the amount of slack, you can change the spider gears, side gears, cross shaft, and the associated thrust washers yourself, if you're a capable mechanic. This requires opening the differential cover, removing the rear axles (at least far enough to get the axles out from the side gears), remove the cross pin retainer bolt, manipulate the cross shaft out, manipulate the spider gears with their thrust washers, out, manipulate the side gears, with their thrust washers, out, then replace the above, with a 'gear kit', which includes the side gears, new thrust washer, spider gears, with new thrust washers, cross pin, and cross pin retainer. A 'gear kit' is around $85 for the Dana 44, 30-spline axle kit. While those parts are out, pry the carrier in each direction inspecting for slack in the carrier bearings and check the pinion/ring gear slack at that time. If you find a bad carrier bearing or pinion bearing, then you should probably find a mechanic to replace those, unless you're a 'very capable' mechanic. After reassembling the gear kit (side gears with their respective thrust washers, spider gears, with their respective thrust washers), cross pin, and retainer bolt, clean the sealing mating surface of both the axle housing and cover, remove the fill plug from the cover, apply RTV sealer to the cover (1/4" bead), attach the cover with bolts, replacing the tags in their original locations, refill differential with either 85w oil or 70W140 synthetic, as desired, approx 2.3 liters, replace plug, and check for leaks. Note: when removing the differential cover, remove all but 2 mid-side bolts, and make them loose. Then tap the very bottom of the lid towards the rear to loosen the cover, have drain pan under the differential to catch the oil. Then remove the 2 remaining bolts and cover. The lid projects below the housing about 1/16" and that is the part of the lid you want to bump on to loosen the cover.
11. Rear disc brake caliper mounting brackets.
12. The sway bar rubber mountings on the axle.

.. and that pretty much covers everything that can make noise on/in the rear end.

13. If a tow hitch is attached, check that for proper attachment.
14.Fuel tank loose, or fuel pump inside tank loose.
15. Spare tire loose, or junk in the spare tire carrier hole.
16. Loose junk in the right rear side compartment (this is actually a CD changer compartment, but if no CD changer is installed, then people put all kinds of junk in there)
17. Rear lift door. Open it a bit and check for side to side play. I've heard of terrible noise on my rear lift gate, and it was the rubber wind seal making a bunch of noise. I wiped it with a rag I sprayed silicone oil onto and quieted that down.