I doubt it... I thought the valves were completely in sync with the lifters and cam, so everything would have to move slightly for a valve to move slightly.

But something is definately up, its no coincedence we have identical running ticks while hot and identical 'drip' tick sounds from the same cylinder area on shutdown.

If a cat is clogged it can cause such great heat that something in the cylinder, or around it, or in the exhaust next to the cylinder, can tick on cool down. Keep in mind ticking on cool down is well-known for cars in general, but it takes a lot of heat to get something hot enough to tick on cool down. So yeah, a clogged/damaged cat could cause that further up in the engine.

Hopefully I have good news after the belt drive changes though.