Brian,
I wonder if the window was knocked out of its track the last time the door was closed or the last time the window was rolled up? When I worked at the Chevrolet dealership we used to get a few second generation cars coming in with "exploding" door glass. The insulation (bumpers) in the doors would wear away or dryout. I had a similar thing happen with one of our street rods. The window broke when I rolled it up, there was a exposed rivet that made contact. P.S.: on a side note, I announced that John Force was at the track (when he was not)on Sunday (for April fools).
Andrew