R.D.
OKAY, I'm a jerk, when I read the title 'Loud Noises' I instantly thought of Steve Carell's character in 'Anchorman' when they guys are arguing in the office, yelling, and he just screams 'LOUD NOISES!!' I love lamp ;)
Anyway, my 2nd daughter was like that for a while. The worst offender: the electric mixer. She would cover her ears and scream! I'd say 'Madison! You've heard this sound a million times before!' And she would keep flipping out. I just kind of assumed she was just more sensitive to certain sounds. She completely outgrew it. I forgot about it until I read your question ;)