[Superman]

These people are telling you to thoroughly check everything out before you go assuming a head stud problem and tearing amotor apart. I agree.

The metallic rattle could be a failing chain tensioner. They say this sounds like a chain being dragged across a metal garbage can. but usually it is present at idle. I think it's more likely that the guts of the CAT have come loose.

I think the dreaded clap may be a different noise and possibly a different source. So, you may be looking for two problems. Look look look, before you decide to rebuild your engine. FWIW, I have been knowingly driving on a broken head stud since last spring.