Valves tapping 96 chev 2500

Truck has 140000 miles. Oil press is at 40 psi. Any ideas of what's causing this and how to fix it?
Thanks

My understanding is, you have tapping noise coming from the engine and proportionate to rpms?
usually, it is not valves. most likely, it is rocker arms/rollers tap on camshaft lobes.
it is my understanding, that this is caused by several things:
1. sticky lifters
2. you, most likely, have pushrod engine. length of pushrods causes slack in the system due to general wear and some bend in them.

I'd start with pouring a can of Seafoam into cranckcase and driving on it for maybe 3-5 hundred miles. It is very safe to do, I have driven on it for 2000 miles in my Ranger. I'd recommend to do this before regular oil change.
flush engine with flush oil before doing oil change(I, simply, buy Supertech oil from W-mart and run it through the system for about 15 minutes, with occasional revvs at 2500 rpms for 20 -30 seconds, to build up pressure and get junk out of tight areas). otherwise, any oil in 0 weight is considered a flushing oil.
you can remove lifters and squeeze them. replace pushrods.
please, try switching to a quality oil.

Thanks. Did the motor flush and changed the oil and the tapping is now gone. Am I supposed to see oil splashing around if I look into the hole when the oil fill cap is removed?

Thanks. Did the motor flush and changed the oil and the tapping is now gone. Am I supposed to see oil splashing around if I look into the hole when the oil fill cap is removed?

with the engine running - yes. don't do it. out of curiosity - why would you even do this? can't see diddly squat there anyway...

glad easy fix worked. next time - run Seafoam in oil for about 500 miles before oil change.

isn't it fun to watch that brand spanking fresh flush oil come out of the drain hole black as a tar? folks that do oil changes at jiffy lubes shoulda see that to sober up....