Sunroof exploded for no apparent reason. Was merging onto a highway in the onramp at about 45mph, very bright and sunny (but not hot, maybe 75F) day. Driver side window was open, A/C off, sunroof was closed, sunshade was also closed. Suddenly I hear what basically sounds like a gunshot right above my head, and since having already heard about this phenomenon happening on a car forum (E90post.com) I regularly visit, I instantly guessed what had happened. I look in my rearview mirror and see large pieces of my sunroof bouncing along on the road behind me. Once I arrived at my destination and got out of the car, I saw the sunroof had exploded outwards. The broken glass was curved up around the hole. From that same forum there are several theories floating around, the one most people seem to agree on as being most plausible is there's a heat/pressure difference between the sunshade/sunroof and the outside of the car. The negative pressure on the outside + the increase of heat under the glass is enough to stress whatever imperfection might have already been in the glass and literally suck it out.

- Dunwoody, GA, USA