okay yeh i have had the cam belt off the othernight as i replaced the cam so belt and sprocket were off. i had noticed today that the noise is associated with no.3 cylinder. when you pull that spark plug lead off the engine does run a bit rough but the noise is completeley gone on acceleartion. Definetley coming from rocker cover area im 90 percent sure of it. what effect would a knackered valve have on the engine. would this cause it to pop under way when slowing down?