differential 'rubbing' sound
 

I just purchased a '02 SL500. 50,000 miles.
I hear a low vibration, like a rub, in the rear on takeoff and reverse.
I''ve had that problem with a Ford Crown Victoria, and it turned out to be the posi-rear.
Don't tell me it's the same thing on this car!!!
btw.
it doesn't happen all the time, only on occasion.
thanks in advance.