Similar thing used to happen at my old job. The fire alarm panel was broken, and would sporadically let out a high pitched alarm. Not the actual fire alarm; no one had to evacuate the building. Just an annoying squeal ten feet from my desk that echoed throughout the classrooms on the floor. If it didn't stop on its own, I'd have to call facilities to send someone, which might take half an hour or more. This happened a few times a week for over a year.