What was that!?

So, Spencer, Tori and I are driving down 1-15 in Utah here and all of the sudden there is this LOUD BANG! Then, we hear glass run off the back of the car and every turn there's a ssshhh on the roof! Our sunroof shattered! Nothing was above us, nothing fell on it. Weirdest thing! And, on top of that it didn't fall into it, it look like it popped out and burst!