I have a 2008 X3, last year the headers needed to be replaced. I just noticed today the tapping noise again and probably need another header job. Is this a problem with all X3's? Luckily I'm still under warranty.
At this late date, I suppose that you have already addressed this problem, but I will toss out a few words. Let us know what you found.
When you say "tapping noise", do you know the source? Is it a noise associated with the exhaust system, a valve train noise, or something else? A leaking gasket at the exhaust header can make a sharp, short sound that may be confused with other sounds. However, once you have heard this sound and indentified it, it is distinctive and you'll recognize when you hear it again.