Today i was cleaning the fresh air vent out before putting the cover back on after the recent paintwork, I took the filter out to give it a clean - Then i got a torch to have a look around and noticed a pile of grass and bits right over on the left hand side, I could just reach in to grab it and it turned out to be an old mouse nest, Somebody had left the air vent open, And mr mouse thought il move in, Could have been a lot worse if he had got inside the car, So make sure you keep it closed when not in use.
Reg