Please help if you can. I understand sounds and vibes are hard to diagnose over the Internet but I need any ideas at this point. This noise is very specific so I think someone will have an idea for me.

The Jeep:
1997 Cherokee 4.0L AW4, rear is a corp 8.25.
Lift is 3in coils in the front 4in custom packs in the rear. NO SYE.
New u-joints and t-case drop (1in) installed. Clean fluid, no obvious signs of issues on the axle.

The Sound:
A "chattering" sound at highway speeds (65+) with NO LOAD on the drivetrain. This is most often when you reach the point that the engine is not decelerating the vehicle but not yet reached RPM enough to accelerate you. It can be simulated by simply putting the trans in Neutral. It is a chattering growl. It is loud enough that it is hard to talk over.

The 'feeling':
Any speed over 55 on acceleration there is a vibration. The vibration does not accompany the sound mentioned above. I assume the vib is from the lack of SYE.

 

U-joint, dry slip joint in Driveshaft or wheel bearing.

 

U joints are both new and spin free. Slip yoke was greased when the u-joints were put in.

How would a wheel bearing be only no-load?

 

A wheel bearing would be doing it all the time. My guess is the driveshaft angle is too great for the u-joints. You probably need an SYE. Your tcase doesn't have the elongated tail shaft housing, so you get vibes more easily than earlier models would.

 

He said at 65, not accelerating, I kinda say that as maintaining speed or sligt decel. My rear wheel bearings when they were starting to go bad would only make noise when in a curve, with side load, either under accel or deccel.
You complain about the least likely issue I listed of 4 possibles. But didn't point out that I left out Pinion bearings or carrier bearings or gear noises or even possible brake issues. All of which could cause some noise as the OP mentioned.

 

I am OP...first off. I was asking for clarification, not criticizing your response. I appreciate any idea. Its not an on turns sound (happens straight ahead) so I don't think wheel bearings. There is no slop in the pinion. I would think there would be with a pinion bearing right? What other sounds/issues would I have if it were carrier bearings?