01 LS Drivetrain whub whub noise

Ok - I don't know how else to describe this noise. Car has 160K miles, and had front wheel bearings done at 90K. Wheel bearings and shafts appear to be in good condition. Trans fluid replaced at 100K and 150 K. Sound seems to be coming from transmission, but not sure. The noise is most pronounced at low speeds when trans is shifting thru 2-3, and can also hear it most when driving with a light foot. The noise goes away under hard acceleration, or at highway speed (maybe road noise covers it up at that point). As vehicle picks up speed from dead stop, I hear a whub whub whub whub etc.. sound. Hit the gas hard - goes away. The tranny shifts and acts perfectly fine. Sound becomes a little louder as the drivetrain warms up. I'm assuming the output side of the tranny on this one, but I haven't been able to find anything like this on the boards. Would appreciate any ideas on this one.

According to Triple Edge Performance on the web, this model year was prone to differential problems, and the sun gear as well. Noise is definatley getting worse, and sounding more like a growl now. Too bad, the transmission still shifts great. I guess its time for a new slush box.

Have you tested for an axle hub bearing being bad?,does the sound change when turning left or right?

Hub bearings were replaced about 60K ago with Timkin units. Noise doesn't change at all in turns or straight. Also, there is no noise noticed when foot is off the gas. Sure would be nice it was the bearings, but they're not giving any indication of being the problem. I will of course check them once I start disassembly.