I have a platter stack from an old Datapoint server, each platter is somewhere around 9". The story, as I’ve heard it from multiple sources, was that a screw or screwdriver (I forget which) fell into the enclosure overnight and dented one of the platters, throwing it out of balance and causing the hard drive to vibrate like crazy. When someone came in the next day, they found the hard drive standing, unplugged, in the middle of the room. People were trying to figure out who unplugged and managed to move this incredibly heavy and expensive piece of equipment, and then deduced from late-night employee reports of what sounded like construction in the server room that the hard drive shook so violently that it “walked” to the middle of the room, unplugging itself.

I can definitely confirm the dent and that it appears to have happened at speed.