Please put my mind at ease... 1999 f250 with 5.4 eng.
When engine is cool to cold there is a horrible noise from right side of engine that I can only described as a desiel knock...I believe it's an exhaust leak...when engine is hot...no longer makes noise

 

Could be piston slap, sounds a lot like a knock and goes away when warm, no real harm assuming you don't go and redline the engine while it is cold.

 

Could you clarify piston slap??