The rear on demand coupling was stripped and serviced by a professional Autogearbox specialist at half the price demanded by main Volvo dealer. This solved the original worn bearing noise from the rear diff. All thought OK until first time on MWay when new noise now from front arose only noticeable at speeds 65 or above but very noisy with (I think) some slight vibration on steering wheel. Wheel bearings checked. Two garages (one a Volvo one can't work out where noise coming from.
Vehicle always serviced and now done 85,000 miles