Yes Mark, I think your question would be better in the general Cayman section but there seem to have been quite a few 'rattle' related posts on here recently for some unknown reason.
Unfortunately rattles can develop for many reasons, items like loose coins or seat belts flapping against hard surfaces, so check for obvious things like that before looking elsewhere. Sound has the habit of actually emanating from a point different from where you're perceiving it and it's always a good idea to have someone else drive the car while you have a good poke around to seek the source, pressing hard on plastic panels, etc. to see if that modifies the sound. Only once you've homed-in on the source can you begin to rectify the problem.
The fact that you get the rattle at 2,000 rpm indicates that something is just vibrating in sympathy at that excitation frequency [~33Hz], so it's most likely a panel vibrating or a cable flapping. It could be the sliding lid you mention or perhaps the speaker grille or something inside the speaker itself.
Jeff
