Its a tapping noise you hear, almost sounds like a desiel engine. The new gen. 6cyl motors all have that tapping noise on cold start ups. Its normal characteristics of that engine and there is no fix for it.
If you take it to a dealer they will most likely tell you the same thing.
I know if there is a certon louder tapping noise then you might be getting a new cylinder head but thats 1 in 500 that happens.