Superformance IRS noise?

[KVenom]

I'm having difficulty identifying the diffy noise in a Superformance Roadster. It sounds like a bearing noise.
It has the aluminum case Ford 8.8. When driving the noise occurs briefly as you advance through the gears. This would be during the brief no load while shifting. It is constant during coasting when out of gear. It does not matter if the clutch is depressed or not. Which tells me it is most likely not the throwout bearing.
I removed the driveshaft to isolate the Tremec 600. Ran it on the lift and was able to shift threw the gears and it is quiet.
I completely removed the pinion mount e-brake, thinking it may be the culprit with no luck.
So it appears to be a bearing in the diffy but I'm not sure. Anyone have any thoughts concerning this?
Again, The noise comes in fairly loud, coasting out of gear, clutch depressed or not.
BTW, A brief history about the car, it only has 3800 easy miles on it. It sat new, unfinished in a shop for about seven years before getting it. Diffy grease was new when the car was finished about 3 years ago.

Thanks!
Terry