I have this problem, too. For the longest time, I couldn't understand why, as my trauma had nothing to do with gunshots, cars, etc., but now I suspect it's because there were slamming doors. Any sharp, loud sounds make me jolt and my heart races.

Sometimes I attenuate to the sound: last night I was at a basketball game and the buzzer made me jump out of my skin until the game and crowd started--then I was not so startled by the buzzer. After an hour, though, I was in sensory overload.