My car began making the same engine noise (tapping noise when accelerating after a cold start) about one month ago.
It has ~48K miles.
I just brought it to the dealer. They agree that there is an unusual noise, but are not sure what to do.
They have scheduled an appointment with me and the factory service rep. in two weeks.
My fear is that he will say the the noise is acceptabe or normal. Believe me it is not.
If anyone has had a similar noise that was successfully repaired please let me know.