I have a 06 gti - has 96,000kms - dead stock and as far as i know in good working order. It makes an audible "tap.tap.tap.tap" at idle.
Whether this is the valves , or injectors i have no idea - but the car is fine. Seemed to be the same noise with all gti's i checked out too.
Overly loud tapping could indicate low oil/stuffed pcv system/loose upper head parts etc.