The problem could be flexing the Panorama roofs are quite large and there could be a couple of reasons for the noise . Recently I had to stop a bloody expensive Mercedes Sunroof which was clicking , I found that the cross brace in the particular model was not bolted in tight enough a few turns on the bolts and it was fine . In your car it could be caused by a couple of things 1/ Higher than recommended air pressure in tyres can cause undue excess road bumps to cause movement in the sunroof housing where its bolted to the body , we have seen in BMW X 5's that they actually fit nylon washers under each of the bolts to allow for flexing in the housing , maybe the roof is not tightened up properly . 2/ Has the car had any mods done to suspension wheel tyre combination from the stock stuff , again we find the most noises from sunroofs are in those cars which have very stiff suspensions in tandem with lo profile tyres . HSV Holden are the biggest problem as the suspension they modify makes the car stiffer than stock , then there are the owners who like I said fit lo profile tyres which are no better than rubber bands .