Diagnose XJ rear diff noise

I bought another XJ last week. It's a 98 4dr sport with auto, bone stock w/ 114K miles. The drivers side rear has a bit of noise now and then. I first thought it sounded like it was in the brake so I pulled both rear drums and cleaned them up a bit and check all the components. The wheel cylinders are not leaking and there is more than enough shoe left. Odd thing was that the drum itself was really rusted around the slot that meets with the backing plate. I chipped away anything that would break loose. The noise didn't seem as noticable, but today while driving at about 30mph on a curve in the mall parking lot the noise seemed to be back where it started. The noise itself pulsates and under firm braking it goes away. That might only be the result of slowing. My next thought is an outer axle bearing. The seal isn't leaking.

Does anyone have any advice on which way to go given the information so far? This is my third XJ and have never heard this noise before.

Thanks

rrrr rrrr rrrr? Does it do it on turns? Does it have a Trac Lock? If so it might be the clutches making noise because the limited slip additive has broken down and needs to be serviced (new oil and additive).

try to have the drums turned. one may be warped.

I swapped out the rear drive shaft U-Joints, still makes the noise a bit.