how easy would it be to access where the fan is to find out what's causing this? i've seen that the air con unit is behind the glove box, which is easily removed. alternatively, would it be better putting the car in to a sparky and having them poke around?

Had the same thing happen in my TF theres three screws under the where the glove box is which is the fan motor. If your lucky you might find a leaf or two but it could more then likely be the bearing in the fan so easier to just go get one at a wreckers