Noisy diff?

[FixYourShorts]

I searched threads first, but didn't see any exactly like my problem. I have a slight knocking coming from the rear end. It only happens when I'm moving, and it increases with speed. My guess is that it is either a u-joint or something in the rear diff. Just so you all know, here is my set-up.

2001 XJ with 140,000 miles. Roughly a 6 lift on 33" BFGs. The lift is a 4.5 RE short arm flex kit with 2" shackle extenders and 1.75 coil extenders. I've got a Tom Woods shaft with a slipyoke eliminator. Both diffs are stock DANA 30 and DANA 35, repectively. I have had this set up for about 5 years. I haven't wheeled in awhile, but when i did, it was my dd, so, I didn't abuse it.

Anyone have a similar noise? Solutions?

I don't know much about gears, but I have an ARB ring and pinion set for the DANA 35 (not installed). Is there a possibility that installing this will replace the potentially problematic parts?

 

[Shorty]

jack it up and check axle shaft bearings, first. If there's any play other than slight "in/out" movement it's time for bearings. Often, you'll hear two clunks/clicks for each revolution of the wheel if these bearings are bad.

 

[MellowFellow]

i had the same problem but once i cracked the pumpkin, i was really low on oil

 

[Johnnie Walker]

My old turdy5 did that, means the gears/bearings are not being lubed properly. Mine started after I drove thru a huge puddle. Got water in my diff.
YOu can check and confirm if the rear u-joint is fubar. I changed the fluid and still the same. Upgrading is cheap enough, and beneficial.