1999 Chevy Silverado has a ticking noise on passenger side engine compartment. Noise comes and goes, almost sounds like an exhaust manifold leak. Also when ticking noise is present the oil pressure guage fluctuates, otherwise oil pressure is normal range when noise is absent.

tdj84; You need to have the oil pressure tested, first. If it's below specs, that could account for the clicking (valve train noise). To test the oil pressure will require removing the oil pressure sending unit and connecting a manual guage.
If the oil pressure is okay, replace the sending unit. But, back to the clicking: Could be a weak lifter. Regular oil changes? Correct oil viscosity?
Loren
SW WA