F11 Whining from Rear

Hi,

My wife's F11 520d has developed a whining sound from the rear of the car. Its at its loudest when at circa 50mph and is present even when in neutral and gets slightly quieter when turning to the right. I've jacked it up and spun the wheels and can't feel any particular roughness in the bearings and our local garage couldn't determine what it was so does anyone have any suggestions?

FYI the car is currently on 133k and has been serviced regularly.

Thanks,

Mark

Cheers for the suggestions. I've since swapped the tyres and then replaced the diff oil, but the noise is still there.

I still think its the wheel bearing so will try another garage, but any other suggestions?