If you are hearing a "knock" that goes away as the engine warms you most likely have a bad connecting rod. If you're hearing the "tapping" of a lifter that goes away as the engine warms it's pretty much normal except that you should hear them all, not just one. If you're only hearing one it sounds like a valve lash setting session is in order.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.