Not at all unusual for S70/C70 models. I've read several similar conmplaints posted here and on VVspy. My 1998 S70 windshield began to crack in a manner similar to what you described, approximately 2 years after delivery. Volvo, of course, ruled it had been struck by some invisible force that left to mark (Nordic cosmic rays?). Two independent glass shops inpected the crack, and gave me opinions in writing that it was a stress crack that originated at an edge defect. I had one of them replace it ($225), and went to Small Claims Court armed with the two written opinions of experts. Volvo never bothered to show up to defend their position, so I won by default.