2003 Rendezvous Growling noise

I've taken my 2003 Rendezvous CXL AWD with 57,500 miles to the Buick dealer and he couldn't help. Hope someone out there can. I get an intermittent growling noise which occurs when the car is at steady rate of speed and the transmission drops down into over-drive (tachometer reads 1100 to 1400 RPMs). The noise is the loudest or most obvious when the engine is warmed up a little and the car is traveling at 30 to 40 MPH. It's driving me nuts. It's not the front hub bearings, I had those replaced at 45, 000.

take back to your dealer....the growling noise is due to weak quality fluid in the rear differential. there is a bulletin your dealer should follow for this complaint. basically you need to confirm the noise is coming from your rear end, and if so, simply replace fluid. I would recommend replacing fluid anyways. use veratrak, available from your dealer. Again, there is a bulletin on this complaint where you local Buick dealer should be well aware of this complaint. I know we are.