Howdy folks. I have a 97, 4.0, 5 Speed, for those that may be able to assist. I've had this TJ for a few months now, and have used the 4WD on several occasions, two of which I've experienced the symptoms below.
The knocking/vibration occurs whenever I have 4H engaged, have little to no traction (eg. mud/snow), and the RPMs are above ~2500. Once I reach higher RPMs it feels as if the transfer case starts shifting from side to side (although I have not been under the jeep while testing this to see what is actually occuring). If I let off of the gas or shift into the next gear the knocking subsides. So far I've only gotten the knocking while in 1st gear.
I've never felt anything like this before, in any vehicle while in 4WD, and am curious if this is something I need to be concerned with, or if this is common in a low traction, high RPM situation.
Any help is appreciated, and I'll be glad to answer any questions I can.