It's peculiar how you become immune to strange noises if you hear them on a regular basis. Slightly off topic, but I live under the Heathrow flightpath, very close to the airport, and don't bat an eyelid when a plane goes over. Yet kids screaming outside get noticed every time.
One day a plane is going to crash into my house and I won't have heard it coming.
Incidentally when I was at boarding school, a disgruntled, expelled ex-student came back and set fire to the staff room. My bedroom was two flights above it, and I heard commotion, but with it being a boarding school, noise was common and I didn't think anything of it. 5 minutes later the fire alarm went off, we were all evacuated and the staff room was burned to a crisp. Being young, we were all quite excited at this, despite having to sit in a freezing cold chapel in the middle of the night for 3 hours with nothing but our duvets for warmth.