[Tannaton]

I'm not clear on why you think there is friction from the rear wheels and what the symptoms are? I get how you might think there is friction setting off if you know the car well but how do you narrow that down to the rear wheels?

Any friction, whether in the brakes, bearings or diff would translate to heat when the car is moving. If the friction is sufficient that you can feel it then that would be considerable heat generated during motorway journey.

FYI older XC90's are susceptible to rear brake calipers sticking which can cause this friction - most owners notice as they smell hot brakes when getting out of the car or have a vibration at speed.