Whining Diff or Wheel Bearing?

[Aidxj6]

Hello forum members, I've not been on the forum for years, but I'm thinking about buying a G reg 4 litre Sovereign with around 89 000 on the clock.
The car is cosmetically very good and drives prwtty well generally.
The main issue I noticed on a test drive was a droning whine from the rear of the car.
The car was sold to its current owner with a new rear wheel bearing still in its box in the boot, and neither the previous nor current owner fitted the bearing - the current owner having hardly used the car over his three years of ownership.
Given the mileage of the car and its good condition, I'm wondering if it's likely to be a worn differential, or if the wheel bearing is indeed more likely to be the culprit?

[andypryce]

Guess could be either, as sound is similar though wheel bearing more of a rumble than a whine, would be worth getting someone sitting in back seat as obviously wheel bearing will be to one side whilst diff would be central.

[Aidxj6]

The tip about identifying if it's central or to one side is a good idea. Thanks, Andy.

[davidr]

I would think that the 2 things would sound quite different. It's a shame we can't be in the car with you!
A wheel bearing is more of a drone that will diminish under braking as the action of the pads on the discs will tend to centralise and stabilise the bearing.
A noisy diff will tend to be more proununced on the overrun as the forces on it change from drive to retardation. The noise will tend to be a higher pitched whine.
I would suggest driving the car at a steady speed and lightly applying the footbrake with your left foot to listen for bearing noise.
After that, drive along steadily while gently applying drive through the throttle and then releasing it so you are loading the forces on the diff one way and then the other. Listen for whining on the overrun.
Having said all that, finding a set of bearings in the boot is a big clue!
Maybe ask the seller to replace the bearings to eliminate that possible issue? If the noise is still there then it points to something more difficult and expensive such as the diff, gearbox or another part of the drive train that may affect your decision to purchase the car.
Hope that helps

[Aidxj6]

Hi Davidr,

Thanks for the descriptive assistance. Unfortunately, I'm about an hour away from the car but, if I do take it for another test drive, I shall try your diagnostic tricks.

Thanks