noise

[rob_a4]

help needed please
after driving 15 miles i get a loud on and off whirring noise,it dont sound metalic
i cant make my mind up if its inside or out of the car
it seems to come from the o/s in the dash area (but sound travels)
if i dab the brakes it stops then starts again
could this be a wheel bearing? or something worse?
just seems odd that it does this after 15 miles (every night)

any ideas

rob