Whining noise is driving me crazy pls help!!

Hey everyone so I'm new to the forum but I have a problem with my jeep and am really hoping I can pick y'alls minds.

So a little background on my jeep.
I have a 1998 4 door Cherokee it has a drivetrain out of a 95 xj the motor has been rebuilt and the trans has been gone through the t case has an SYE but I'm not sure it it's ever been gone though fully. It is long armed and has a Dana 30 upfront and a xj 44 in the back both are geared 4:10 with auto lockers.

So onto my problem:
A few weeks ago my jeep started making a high pitched whining noise I can kinda hear it at lower speeds but not really. It gets really noticeable over about 40, the pitch doesn't change with speed but it does get louder the faster I go. All the fluids are fine and there's no grinding in the noise.
I've tried a ton of diagnosing and haven't got anywhere. I replaced the front wheel hubs and pulled the rear shafts and they looked fine so I packed them in grease and put them back in. I've also rebuilt both driveshafts completely this week. The noise would appear to be coming front the front half of the cab but you can only hear it with the windows up and it seams to move around when you move your head in the cab. The noise doesn't go away by letting off the gas,getting on it, kicking it out of over drive, kicking it in to neutral, or even Turing the motor off in neutral while coasting at speed. It isn't affected by putting it in 4 wd or pulling the front driveshaft. I've even taken it to two shops and had mechanics ride with me one was even a jeep certified mechanic and he had no idea the other place even put it on a lift and ran it at 50 but on the lift there's no whine in the cab and they checked everything with the thesascope thing and couldn't hear any noise at all.

It is driving me crazy I'm one of those people that fixes every squeak and noise. So I need to find this. Also my main problem is I'm a student at college and can't just drop a t case in my apartment parking lot to check it if it wasn't for that I already would have.

So I'm asking y'all if you've ever experienced this because I could really use the help.

I honestly sounds like you have a bad carrier bearing. You can have a bad bearing with no metal in the fluid. I'd ask another shop to look at it. I'm pretty shocked they couldn't find it on a lift if it's as obvious as you say. Or turn the radio up and the problem will present itself later.

It's your rear end. Depending on what the issue is, you may not hear it if the wheels aren't under load so running it on a lift may not catch it. Take it to a shop that specializes in axles and they will find it.

Sounds like the rear wheel bearings. If they did not hear it on a lift or by jacking up the rear and putting in in drive then it is related to the weight of the vehicle.

I though about carrier bearings but every time I've heard bad carrier bearings it's been more of a grinding noise. Plus I would figure they would have heard something with the probe.

I also thought about rear wheel bearings but they are in great shape and I would at least think that packing th I grease would have changed the noise for a little bit.

If you're repacking bearings, you can pull a diff cover to inspect the gears and at least refill with new gear oil. I hear folks use a Lucas product to quiet them down too so that can help you diagnose. If that's the case, you can at least know you have a regear in your future.

If it was a gear oil issue wouldn't it make the noise in the air as well?

After driving it around some more today I pretty firmly believe it's either the trans or transfercase because the noise definitely isn't coming from the back half of the vehicle.