What should I do about a noisy valove?

You can try Marvel Mystery Oil...

I did but it did not work.

Have you tried an engine flush system?

if that don't worked you need a valve job...

Try ( Lucas Engine Oil Stablizer ) Had a friend his engine was tapping like crazy I told him I do not know if this will work but lets try it. Changed his oil left out one quart and added the Lucas and with in 30 minutes tapping was slowly going away and with in 45 minutes to a hour the tapping was completely gone. That was 2 weeks ago and it still sounds good.