O.K. When it's open is it noisy? Are you sure it's fully closed? There are rollers and followers in the tracks on these sunroofs that lever them into the closed position when the mechanism reaches the end of it's travel. I had this problem on my BMW. A screw had fallen out of the track arm on the driver's side and the roof was not able to lock in the closed position. It looked closed but it really wasn't. Biggest problem fixing it was removing the headliner material from the panel to get at the loose screw.
1987 BMW 325