What's that noise.

I have a 1999 XJ Sport. I bought it used with 56,000 miles. It has the Select Trac transfer case. The noise that I describe is in 4WD only (4 Full or 4 Parttime) and not in 2WD. It had a bearing noise in 4WD. I had the front differential bearings changed. It helped some, but not 100%. I then had all bushings replaced with polyurethane bushings. The grinding type noise in 4WD got noticibly worse. I took it to the Jeep dealer (They had replaced the front diff bearings also) and they said it probably was the front bearing in the transfer case. It was replaced, no difference. The tech took the transfer case apart and said it looked OK. At that point, I was able to get Chrysler involved and they said they would help. To date, the front diff bearings have been replaced, the front ring and pinion and case have been replaced, the transfer case has been replaced and the grinding type noise is still there. Nothing has changed. What is it. Did the new bushing change the geometry of the front end? They are talking about changing the tranny, but I don't think that's the problem. Anybody have any ideas? Remember, DCX (Daimler-Chrysler) is doing this. I await somebody's
expertise.

I'd like to bump this up. I'm having the same issue with my 98 classic. It's only got 40k miles on it, so I find it odd that stuff's wearing out. Only in 4wd. I have the 231, but you described my issues pretty good. The thing I don't understand is...why only in 4x4? With the non-disco shaft, everything should be spinning whether or not I'm in 4wd.

Somethings like the front axle U joints, don't have any/much load on them, unless it's in four wheel drive. I've had dry front axle U-joint caps that barely made a noise, that would get pretty loud in 4X.
Pretty much the same thing with the front driveshaft and diff/axle/hub bearings. One thing that will help narrow it down, is if it's louder during a turn, when accelerating or decelerating.
Drivetrain noise will drive you nuts, the sound travels and is often the loudest at the transfer (right under your rear).

had a similar grinding noise. was coming from my centering ball on the double caradan joint on my front DS. Had to peel back the boot as best I could and "inject" grease in there with a syringe and part of a pen to use as an extension. Sounds like those techs aregoing to spend a lot of money the don't have to. Have them take out the front shaft and try in 4WD again without the front shaft (don't worry this won't hurt anything) if noise goes away i will bet good money that or a u-joint will be your problem.