Gearbox

Have recently bought a 2010 Traffic 115 dci test drove the van and it seemed ok until a whine came into it and it only comes into it at 80 kph and gradually gets louder as you pick up speed,thought it might be a bearing but when I jacked up the front wheel on each and getting the same whine once it gets up to 70-80 kph and also when I clutch at these speedsand knock it out of gear the whine is still there until it drops in speed.Any Help Please.