I am jittery of everything I hear now:
Fire engines and ambulances, although I am near a firehouse, the sirens are going nutso right now!
Airplanes, alot of those too near O'Hare but nervous nelly I am, especially hearing choppers in the wee hours
I live in a medium-sized metro (Kansas City area) and I've heard a lot more sirens in the past few days too.