I have an 07 lmm. When I start the truck and it's at idle I can here a tap tap tap noise coming from the engine. It's very noticable when the motor is cold and pretty much goes away after the engine runs awhile. The tap noise is not a constant tap, it might tap 2 or 3 times then stop for a couple seconds and then tap 1, 2, or 3 times. I can,t hear it from the top of the motor, really just from the drivers side front fender well. Any ideas what this could be? Valves?