Grinding, " diesel " noise under valve covers

Whoops... so just put my ear down to the pipes? It definitely isn't where I can hear it standing there. Or do I put my head on the pipes, while cold? No
.. wait,, that vibration would be all I felt... crap.
You're not gonna hear it through the pipes. You know why? Because of the.......wait for it........EXPLOSIONS in the cylinders. Hear it through the pipes. Now I know he's crazy.