What is the worst sound you ever heard, that turned out to be a false alarm?

If it counts, then:

After I moved into my first rented place, at night I heard some horrifying noises from upstairs. Like if some heavily drugged guy was growling or something like that. I couldn’t sleep that night, and the noises always showed up every night.

Turns out my upstairs neighbour had sex every night, and he makes weird sounds during that.