That is why I said to look for the obvious like wheel bearings and wheels. It is unlikely to be the gearbox, but it is still a remote possibility as although the gearbox is not driving the wheels whilst in neutral, the wheels are driving the differential. But as I said, it is 95% unlikely to be gearbox.
Also, go underneath the car and look at the CV joint boots to see if one is split. This would be indicated by black grease (Molybdinum dysolphide) (Spelling???) being thrown everywhere. If this is the case, then the associated CV joint could be dry. This would also cause a noise when the car is being driven and steered at full lock. You would get a clacking noise.
