I'm having this same sort of issue. I can only hear it not really feel it. It's sort of a whirling binding/ light grinding sound. I've never experienced anything like it before so it's hard to explain. Only happens at lower speeds (30-40mph).

 

Might be time to change your diff fluid.

 

Rear differential clunking noise. Only when it's warmed up. When it's cold no noise. Is this a symptom of diff fluid breaking down/need changing?
I have a 94xj 4L 3 speed auto.
Your thoughts please.