Paul V
The only thing that I can see is if it is a whining or singing sound when cold it would probably be the intermediate bearing on the drive shaft.
however:
The halfshafts, differential and pinion bearings can all produce the noise. Try driving under load and if the noise appears it is probably the rear pinion bearing. If it whines during coasting, it is more than likely the front pinion bearing. Good luck!
PS: let us know what happens.