Ok I have a 2001 Ford F150 4.2L standard transmission, now the problem I’m having is after my truck warms up, I hear what I can say sounds like valve tapping sound as the truck is in gear and traveling at any speed. The more gas I give the noise gets louder and tends to disappear once I settle on a speed. Now when I take the truck out of gear and rev the engine there is no tapping sound. So all that being said the noise is not there at idle nor is it there with the clutch depressed, only while there is a load on the engine.

 

Exhaust manifold gasket