+1....^ Hit a pot hole on my way to Petit Lemans last yr. -I had to turn around and go back home . Then went to a shop the next day to have it inspected/ or repaired. Turned out the out rim (see image below was slightly bent in). They used a torch to repaired it; they tested for leaks/cracks and everthing else. +1 with OP it sounded exactly like a gunshot.