ive got a bit of a knocking noise only at certain revs, can a worn cam knock/rattle intermitently or would it make a noise all the time

is this more likely to be tappets?

if so should tappets and cam be replaced together? or can you get away with just slidding new tappets in?

its only been like this since its came back from its mot where i suspect they were reving the nuts off it for the emissions test