rod knock

could a rod knock sound like a tapping, and would you not hear it until the truck warms up, or would you hear it more when its cold.

A "rod knock" will start as a "tap" possibly. But will quickly increase in noise if it is in deed a rod knock. Oil viscousity may hide rod knock or lifter noise when the engine is cold. But a real rod knock will only increase as bearing degenerates, where lifter noise tends to stay constant.

If you've got a light tap, it's most likely a lifter. Jrmcs is right, a rod knocking will get louder very quickly.

My 3.9 pings but only when it's warm.