It’s a military thing.

http://espn.go.com/blog/playbook/fandom/post/_/id/6544/how-flyovers-hit-their-exact-marks-at-games

My wife was working a homecoming game at Texas A&M – Commerce when two F16s did a flyover. One went vertical over the stadium and hit afterburners. Every car alarm within a half mile announced the aircraft’s thunder.