1999 sls strange noise(hummm)

I noticed a whine comming from the tranny. The whine doesn't change with engine rpm's, but does with speed. While moving if you put the car in neutral and rev it the whine doesn't change. Anyone have any ideas? Car still shifts fine, just an annoying sound that we would rather get checked before something happens. The best description for the sound would be like snow tires or mud tires on a highway. Also when I turn (even slightly to the right the sound goes away)--Any suggestions would be extrmely helpfull

turned out to be passenger side front sealed bearing

Thank you for giving a response for your own question. I am actually having this same problem now and wasn't sure if it was a wheel bearing due to the fact that it wasn't high pitched but your problem definitely sounds exactly like the one that I am having now. I'm going to get it checked out tomorrow morning