Low Pitch Whining @ Rr Axle???

[MRDANGERUS]

My girlfriend's 2003 Santa Fe, 4AWD, 33,231 gently driven hwy miles, developed a whining sound coming from the rear axle area. Sound is speed dependent. At 15 MPH is low and hardly noticeable. Frequency of the sound is going up when the speed increases. Very pronounced at 30-40MPH. It does not change with acceleration/deceleration.

I rolled the vehicle downhill with engine off and trans in neutral= the same results.
It seems to be rear driveshaft associated. Perhaps pinion shaft bearing going bad?

I took it to the dealer. They changed rr hub bearings and overhauled the brakes. It took them 3 days to do this (?).
It did not fix the problem.

ANYONE: ANY IDEAS, SAME PROBLEMS, TSB-s?

[DSHornet]

My "new" (to me) '01 Santa does the same thing - noticeable whir at speeds around steady 35-50 or so, but my noise goes away when I accelerate or slow down.

On another message board I saw a post from a mechanic that said the rear differential does this as it wears but doesn't seem to be a sign of imminent disaster. I changed the rear diff lube a few weeks ago and it made no difference. However, I did notice that the rubber bushing that holds the center support bearing for the rear propeller shaft was a little slack - I could move it vertically with my hand and see the rubber bushing move in its bracket. I don't know if that is normal or if it should be tight in the bracket, in which case it should be replaced.