rattle noise from top of engine

hi all, my 4.6 has developed a weird noise from the top of engine,its like a spanner in an empty tool box kind of noise, is worse when cold, but still there when revve it when parked,
its just passed its mot no problems, it got compression tested last month all ok, ive just changed the oil and filter still same noise, seems to be drivers bank and from the top of engine, it uses water not loads but a enough to top up every few months, is only done 74,000 and is a 1997 model
I`m worried this as a slipped liner, how ever am hoping could be something less drastic, ,maybe cam wear ? injector blocked ? its quite violent the rattle but does go away

all ideas gratefully recieved

cheers

Take the Rocker cover off and take a gander.....maybe some on the rocker gear...

If it is not losing performance though I would doubt it is Rocker related....

Possible slipped liner, they can tap when running - not sure about rattle though.

Maybe a leaking tappet causing the rocker to rattle. If it goes away that would be my guess.