Mine does the same thing. I've got a 2005 with the panoramic sunroof. The rattle disappears when the cover panel is closed.

From searching other posts on this topic, it seems that BMW has issued a TSB (technical service bulletin) on this problem, and will fix it for free. One post said the entire headliner has to be removed and replaced as part of the fix. That sort of scared me away from doing it. I may change my mind at a later date if the rattle gets worse.