1992 AW4 Strange Noise

Hey all, long time reader, first time poster!

I have been reading through this forum, as well as a dozen other jeep sites, and haven't been able to find a thread that specifically targets my issue. I just purchased my second XJ, a 1992 Laredo with about 220k on the clock. I took it on a 4 hour round trip, with varying speeds from 60-75 mph, and I started hearing a noise.

Between 50 and 60 mph, I hear a faint whining noise regardless of throttle position. No real vibration, but a definite noise, and it sounds like it's coming from the trans tunnel.

After 60mph, the only time I hear it is on deceleration (foot not completely off the throttle, but not pushing it either, think maintaining speed downhill on the interstate). If I let off the throttle, it goes away, and if I press the throttle, it goes away, and if I change nothing with the throttle pedal, and shift it into neutral, it goes away.

I have read other threads regarding axle noise, and varying trans noises, but nothing seemed to fit this bill.

Thanks a ton in advance for the help!

Any thoughts?

how is the rear pinion bearing? rear end in general ?
how are your u joints on the rear DS ?

I heard the same noise on my xj and it turned out the T-case was low on fluid, I topped it off and it's been quiet since.

One thing to be aware of when you start hearing noise in the trans tunnel area is check the u-joints, up above 45mph or so it was feeling like driving on a rough road, ended up my rear u-joint had turned it's bearings into a substance resembling strawberry chunky peanut butter.