Rear Window Defogger problems of the 2007 Chrysler Town & Country

2007 Chrysler town and country. While driving on a residential street at 30 mph, the rear window "exploded". There was no other car around, no other car passed me by that would have kicked something up from the roadway. There were no people, kids or animals in the area. Temperature was 29 degree's. The rear defogger was not turned on and the rear wiper was not on. There was a hole approx 12" x 6" on the upper left of the window - the rest of the glass was shattered. The glass fell into the van on the floor. There was no object (rock, ice, snowball) in the van. Nothing could be seen on the road. The window was replaced at a cost of $358. 27. This happened on 02/15/10. In August of 2008, this van was sitting in the driveway. We were inside and heard a loud "crash". The rear window had exploded leaving a large hole in the glass. There was no object in the van or on the ground around the van that could have caused it. The window was replaced. I called the dealer regarding this recent window and was told there were no reports or complaints like mine. I placed my problem on the edmunds forum and received a response from 1 person who claims their tail light enclosure explodes. His mechanic claims it is due to excessive vibration of the tailgate.