My 2001 Passat 2.0s saloon has recently developed what I can only describe as a humming/droning noise accompanied, occasionally, by a slight vibration felt through the steering wheel. This noise is most distinct at around 40mph but at higher speeds it also seems to oscillate a bit,from the near side wheel.

At first I thought that this might be caused by my front tyres out-of-balance front driveshaft, or perhaps a shot wheel bearing. However as this noise has been present for around 1,500 miles now I think that if the noise had been driveshaft or wheel bearing related then this would have manifested itself much more obviously by now.

The noise doesn't seem to be getting any worse and, in fact, sometimes it's hardly noticeable. It also seems to make no difference if the car is in gear or freewheeling.

Any ideas?