Fourth rear window in 3 years to shatter on its own. Different weather conditions on each day it broke, car not sealed tight ie. window open. Once while in car driving it broke. Glass company can't figure it out. Every thing checks out all right, hasn't been in an accident.
Looking at the shatter panel on the window, can you see an area of stress? Do all the windows break the same way? The weather might not play a part, if say you have something pressing or inadequately putting abrupt pressure on the glass. I have seen it where a screw was placing pin point pressure, and breaking windows.