remdev

All,
I have a 98 Jeep Cherokee (XJ) 4.0L with 243K miles on it and it has a noise that I can’t pinpoint. Before throwing time or money away, I thought I’d check the forum for insight or advice. All thoughts welcome.
TC: NP231J
Transmission: AW4

The noise is only present when moving
The noise seems rotational in nature and gets louder with speed
The sound seems to come from the front of the transmission hump or back of the engine compartment while driving
Sounds like gearing rattle or rough bearing to me. Could be a dragging (like a stretched TC chain rubbing the housing) sound but tough to tell. Not a popping, hum, howl, or tic noise
No noise at speed with rear raised up
Differential, Transmission, and xfer case fluids are good
In Park at 2K rpm no noise and engine sounds good
Foot on brake and give gas, no noise
Put in Neutral while driving, rpm’s drop but no change in sound
No shifting issues when driving on the road
Putting in 4WD no issues
With the jeep on stands and indicating 40 mph (wife at the wheel), I was not able to pinpoint the noise (engine, trans, TC) using a section of garden hose. Nope – didn’t get under it. I was already spooked enough. However, the noise could be clearly heard when sitting in the Jeep
Just did the brakes and no wobble in the wheels
No extra noise going around turns so probably not a wheel bearing
Front wheel ujoints are fairly new
Front and rear shaft ujoints are new
Problem existed before the following as well
New motor mounts
New trans mount
New exhaust system to include replacing the cracked header.

Any thoughts on cause or approach to determine the the issue welcome!

PatHenry

Sounds like you've got a thorough preliminary checklist completed.

While I doubt it's the cause, have you checked for the common "loose flexplate bolts" issue that you automatic guys frequently have?
If nothing else, worth at least checking out.

My gut feeling is that it's bad news (like a tranny or transfer case bearing), but without a better pinpoint on location it's hard to tell.

If it were me, I'd grab a mechanics stethoscope and see if you can get a better check while jacked up. The tip on the scope should reach easily to the t-case or tranny case without you having to crawl under it while it's jacked up.

Maybe also check for play/noise at the pinions. Noises are notoriously sneaky about where they seem to be coming from.

Maybe rear wheel bearings?

It sucks that you can't truly simulate driving loads without actually driving.

What axle is it on the rear?

remdev

My issue turned out to be the front differential. I have not torn it down yet so not sure whats going on with it; but at 243k I'll just rebuild it.

gat

I wondered about that myself.