I have a 2000 Tj with a Dana 35 rear and about 85k on it.  I just but on bigger tires 31x10.5's.  Recently I started noticing popping and creaking comming from the rearend.  It is especialy noticable when I am starting after a stop or taking off on an up hill It was realy bad when I had some friends of mine in back for a ride.  It was creaking and popping like an old ship under stress.  My guess is that my OEM limited diff is dying or dead.  Would changing the fluid help?  maybe the friction modifyer is done or the viscosity of the oil is killed.  I am still new to Jeeps and working on vehicals but I know I can open seals and change fluids on them.  Does any one think this will help or is it time for a diff upgrade? I can not afford a selectable locker and a belive a Detroit would be too harsh for on road.  I have been looking into Aussie lockers and people seem to love them.  Any feed back?   This jeep is not a daily driver just my non practical vehical that I enjoy driving and taking camping.  

I would change the fluid first and see what happens. You know what they say, start with the cheaper end first. A friend of mine has a 2000 Dodge Ram with about the same milage, his rear was squeeking only in reverse...turned out his fluid was low.  

Possibly a bad ujoint. If your hard on and spin the tires you may have lost clutchs. When this happens it tends to take the bearings out as well. Grab your rear drive shaft and push in each direction of the bearing caps. If there is play replace them. Its easy to pop the end of the shaft off and look under the free caps of the ujoint. To check clutch steels pop of your diff cover and look at the fluid and see if there is foriegn material there. If this is a first time oil change then it will be nasty. Next is easiest thing is to change your clutchs and steels. Which requires you to pull out your carrier. Be sure to keep track of the shims on each side of the carrier. This is the part of set up of your differential. Mixing them up or not putting one in will mess things up. I cant imagine you would have deystroyed it with camping. Don't try low lock burn outs on dry pavement with it. With 31's your waiting on the fuse in that grenade to burn down.  

This is an old thread but for future reference...

Sounds like u-joints in the drive shaft. U-joints click, pop and clunk. Bearings whine and the whine only changes with speed.

U-joints pop and clunk and change when the angle changes. As in load hieght change, acceleration, braking, and putting in gear if an auto trans.

If the spider gears are bad, they too can make poping sounds but they make noise while turning not while going straight.

If anything inside the diff is bad enough to make clunking noises, stuff is really wasted and you'd really know it.