Intermittent Diff/Bearing noise - Not an easy one to pinpoint

Had a noise appear after our last 4 x 4 trek that I am unable to pinpoint at this time.

I replaced the back brakes as the shoes were worn completely and the drums were U/S - I was hoping this may be the cause - It was not

Seems to happen at random at lower speeds and more likely on a bumpy road or at deceleration. All of a sudden a substantial Bearing/Gear noise like a Bad Cruiser diff starts up and may continue for a short to medium distance. Applying a bit of power does not remove the noise.

I have ruled out the front diff as I have free wheeling hubs an I am not in 4 x 4. I have not ruled out a front bearing but I feel its not likely to be this given the random nature of the noise.

The noise continues even if I throw it out of gear and coast, but stops before I bring the car to a standstill.

I had a good look at the tail shaft and uni's and mid bearing seem fine.

So what is the chance of Random rear bearing or diff noise? In my experience they usually carry on and not stop before you can pinpoint the direction of the noise.

I like to try to diagnose before delivering to a mechanic, but this time I may have to pay to find this one :-)

Cheers Tony