rattling noise from sunroof

[kvin]

Hi guys, I have an X5 3.0 with sunroof. recently, I have noticed that there is a rattling noise when the roads starts to get bumpy. It is as though something is loose and keeps rattling (sounds like plastic knocking plastic). It is not really loud, but it can be irritating. If I hold the roof whilst riding through the bumpy roads, this rattling noise disappears. Brought it to my dealer and they did a road test but heard no noise.
And it rattles louder when the cover panel is open to expose the sunroof.
Did anyone on the forum meet with this problem? If so, can you advise what was done for repair?
Thanks.