Both the insurance people and I assumed I must have run over a large rock, and I did run over a 5 inch diameter rock bounding off of a truck and heard it make a whack sound under the car.
I did not see any damage when I pulled over, but no one could come up with a better idea of how the damage could have happend. In the end they just fixed it.
It sound like we have a structural problem with the Z3 chasis. We should do a little more work on this.
Why not just weld it with a little more material attached?