Please help identify this rear end noise source

I've been a long time lurker here, and read quiet a few threads in bringing my "craigs list special" XJ back to life. Ive done a complete overhaul of everything under the hood, and interior and now am stuck with one last problem to resolve (at least for now lol)
So, original symptoms are that I would notice some vibration from the rear end while accelerating 35-40 mph and then it would clear and come back if under heavy load above 65 mph. But, much louder noise (like mechanical grinding & vibration) would be heard when decelerating.
Today I finally put the jeep on jackstands and accelerated the wheels to be able to spin the wheels and get a closer look at what is happening. I will say that I have replaced the ujoints and the noise has stayed the same. Noise to me sounds like it is still coming from that area, though ...
I am planning on replacing the driveshaft (mine has a shiny spot on it from where a weight or a sticker used to be), but I was wondering if anyone could shed any additional light on this.
It is a 1999 Xj, 4x4 with 156k miles on it. Rear leafs have been replaced with heavy duty ones (but I am not sure that it resulted in any lift).
Video attached https://www.youtube.com/watch?v=J2Ri6xxWE4s

That.....is.....weird.

My first thought is something tinny like a drum rubbing against a backing plate or a parking brake cable bracket or something vibrating. Have you put your hands in various places around the axle housing while having someone rev it up like that? I wonder if you would be able to feel the vibration and narrow it down by feeling around, or watching from underneath while a 2nd person duplicates the noise. Of course, being very, very careful. All I got. That's a weird one.

Thanks for the ideas. I was doing it by myself so didn't have a chance to feel for vibration - but, will try again tomorrow and see if that helps me narrow it down.
I was unsure at first (by hearing the noise from inside of the car) if it was transfer case, drive shaft or the diff - but, I can definitely hear it coming right from the aft ujoint/diff area. But, those are new, - and I also do not feel any play in the shaft there ...

What does the differential fluid look like?

Have you ran it without the tires and drums?

If you do this, note that your rear brakes will push all the way out without the drums, so you can just put it in neutral and let it slow down to stop.

Buy a mechanics stethoscope. You'll be able to narrow the noise down much more accurately. They're cheap.

Looked to me like the pinion moved a bit...as in up and down, when it just started spinning and again when you stopped. Have you opened up the pumpkin yet? Have you ever changed the rear end fluid?

Otherwise, have you eliminated the possibility of the exhaust rubbing on anything, like the cross member or the rear leaf spring?

differential fluid looks fine. Still looks clean and no visible metallic particles.. As for the movement - I did notice that the yoke moves up and down too during acceleration, but I figured that some of it would be normal due to siting on leaf springs. I am not sure how much of the axial rotation is considered normal. Leaf springs are recently replaced and new, and all bolts are tight....