Wow, sounds like a big rock! I had something from the end of a semi hit my windshield last fall, it just barely chipped /nicked my windshield. But yeah, I have heard 1 or 2 times something that sounded big hit my windshield (I do a lot of interstate driving - i know, go ahead and frown, but hey- these cars were made to be driven right? hehe) and the sound was pretty big, but never did anything, it sounded like it would, but our windshields are pretty tuff, I feel safe with it and in our cars in general- 4/5 star crash test ratings in all zones!