I had a rattle that I thought was my sunroof, I thought it was the slideing shade but in fact it was the trim that surrounds the alarm interior sensors. it's the grill with slots in it just by the interior light. The clips that hold this trim in place are what rattle as they are metal clips inserted into the plastic trim. if you remove this trim it is so rattly that you can use it as a tamberine. A drop of superglue on each metal clip where the clips are attached to the trim will sort it out.
I did actually make a thread about this.
Here it is>>>>
http://www.seatcupra.net/forums/showthread.php?t=238904&highlight=fixed+rattle