Weird knocking sound of the cb650c cam chain tension

I've been trying to restore an old 1981 cb650c. But I have come across a weird knocking sound from what I believe to be the cam chain tension, this knocking sound becomes muffled if I hold down the clutch, it is really bugging me as it is very audible at lower speeds. Anyone able to help?

knocking from the chain? cams maybe, valves maybe, piston slap, wrist pins, not likely the chain. Pull the tensioner and see what shape it's in. JMO