If you get a metallic ticking sound coming from the cylinder head area don’t immediately assume it’s a valve clearance (tappet) or cam chain rattle, it’s very often an exhaust gasket leaking, strangely it can sound exactly like metal tapping on metal.
so if you get this “tick, tick, tick” sound get an industrial stethoscope (or a length of flexible tubing) , and with the engine running on tick over listen to each header joint individually, move the end of the pipe around the circumference of the pipes where they join the engine and if one is blowing you will clearly hear it.
whether it’s then wise to remove the headers to replace the seals is up to you, the studs can snap if it’s all rusted up so sometimes it better to put up with the ticking!!!