The activity that is taking place on the floor directly over your office or cubicle. It sounds suspiciously like orangutans wrestling aligators in a dumpster.
It is still less annoying than some putz failing to turn off the all-page while they shuffle papers and manipulate their stapler.
Office Drone #1: "What the hell is that? Sounds like a train derailing."
Office Drone #2: "Must be the new full-contact accounting system."