A valve tapping or knocking noise may be heard from the top end after the engine cools down (the vehicle is parked overnight) or after it has been idling for an extended time. The tapping noise will decreases as the vehicle is being driven or if the rpm is held above 2500 -3000 RPM. This may be caused by the valve
Hydraulic Lifters (HLA) bleeding down as the engine cools or when the engine has been idling for an extended period of time, creating excessive valve lash clearance.
