growling sound when lifting throttle @ 55mph +

Newby here, I've had a dozen questions about my recently aquired '90 Limited but have had them all answered by searching. But this one I can't find: While traveling at higway speeds if I lift off the throttle I here a growling sound that goes away after I slow down to about 55. I had a similar problem in a Shelby Dakota that and ended up being the OD. Is that a good place to start here or could it be TC or u-joints or something else altogether? Any and all thoughts are appreciated so thanks in advance.

I'd check the u joints first.
and open up the rear diff to see if there's any metal shavings in there, could be a pinion bearing.
check the driveshaft for lateral play while it's attached to the pinion and the t-case output.
assuming it's 4wd.

I had a similar noise and it turned out to be a pinion that was self destructing. Try pulling the rear driveshaft and run on the front only and see if the noise goes away.

LOL! what a coincidence - I also have a 90 XJ Ltd (is yours red by any chance?) and had the same thing happening. I was pretty confident it was something in the rear end, likely a pinion bearing on its way out. I never did open it or check it out as an 8.8 swap was always in the cards and that is now done. I still have the d35 with the growl so I might open it up and see what's up in there....if I get the time.

I actually haven't even driven it on the 8.8 yet (still fabbing rear shock mounts) so I don't even know if that was the cause of the growl.

Thanks for the input. I guess I'll start by checking the rear end. I like the idea of taking the driveshaft off and driving on just the front, that way I can go ahead and replace the u-joint. If the noise goes away then comes back I'll know it's not the u-joint.