i seem to remember my xj's 8.25 doing something similar once just before the carrier broke in 2 & the passenger side axle shaft launched out of the tube. popping & a shimmy at speed. but you dont get up to speed in this jeep. turns out that one of the c-clips broke & that ruined everything back there. just a thought. at any rate i did that on a budget & i did not change out the pinion gear & it would sound like a machine gun going down the road & it would make a ton of noise in 4wd. all that was wrong with it was a couple of little nicks in it.
what axles are you running?