Whining sound between 35 & 40 mph

Is this car a all wheel drive? ie . 2.5 or 3.0 petrol. if so they suffer from transfer gearbox problems the normal being all the oil has leaked out from the drive flange and the transfer box bearings have failed, or it could just be a wheel bearing noisy support the car on stands with all 4 wheels of the ground and get someone to run the car up to 40 mph then walk round the car and listen to each wheel in turn. if it is a auto the gearbox is also suspect. good luck