AU IRS diff, humming like a 747

[BuckTooth]

Hey guys and gals,

I don't have the faintest idea on what it could be so i'm asking the AU gurus for help.

I have a 2002 AU XR8, story is i've had to replace both the wheel bearings before, but now it has a terrible hum in the rear. I drove to griffith nsw, about 3hrs from home, I had 2 new tyres fitted to the rear of the car. I then drove home, 3hrs again, but when i reached the 50km signs on the edge of town and backed off i picked up a very loud hum in the rear end. It literally does sound like there is a jet in the boot trying to take off. I suspected maybe it was the new tyres so i did a front to back rotation but then upon road testing it the noise is still there and still very noticeable, How ever it is only from inside the car, i've driven past someone standing beside the road for me, and they heard nothing.

I pulled the 2 rear uprights of and tested the wheel bearings separately to the car and found no fault with them.

So just looking for suggestions on what to check next.

Cheers Doug