454 Crusaders - clicking noise from front of engine

Long-time lurker, first -time poster. Many thanks for all the help I have gleaned from this board over the years. Currently have an issue I've not seen discussed before and can't find addressed in a forum search: I am getting a rhythmic clicking/snapping noise from the front of my engine. It is consistent with current revs, doesn't disappear with higher revs and has continued for some time with no noticeable effect on performance. Tried disconnecting peripherals (raw water pump, circulating pump and alternator) and noise continues. Engines: 1988 454 Crusaders, 800 hours, heat exchangers, no oil leaks evident. Any thoughts?

Possible fuel pump. The rod that actuates the pump can make noise when the pump is worn or the rod sticks slightly.

Timing chain or gears slapping on the cover.

Either area is a possible source....I'd suggest getting a good mechanic's stethoscope to narrow it down...

Hey guys, finally got this sorted out and wanted to post it for resolution. Never could narrow it down with a stethoscope and wanted to avoid tearing the top end down. Got a solid gas engine guy on board, he listened for a minute and nailed it - a blown exhaust manifold gasket. Replaced the gasket, all is well. Many thanks for the helpful suggestions, glad it's settled.

And less CO in the ER! These leaks sound just like metal hitting metal, i've had them too.