Hi John, thanks for the reply, Its a single knock as the pedal starts its descent, and it doesn't matter whether the engine is running or not, seems to be louder under the dash than under the bonnet, but I can't pinpoint it, I've operated the pedal by hand with my head down there and it doesn't happen, it's like the pedal is pushed at a different angle with my foot and this causes the knock, its a very strange problem, hence my asking on here if anyone else has had this problem