MGB Annoying clacking noise

This deeper clacking noise at tickover is annoying me. I'll have to track it down. As it is fairly slow I am thinking something in the cam drive, maybe a follower. Or maybe the distributor.
It's not really a video. More of a sound file.

[@chriswatts4313]

Obviously tappets

[@robertwoodliff2536]

Mmmm.....sounds like a little feeler guage afternoon therapy.

[@foleybrown]

But it turned out to be a badly fitted piston. New rod and piston solved it.

[@markgonzales7572]

@@foleybrown How did you diagnose that? Trial and error!? Sounds tedious!