Re: Okay, this is a weird question

Current theory is that it's something in the electrical closet.

I stopped by your office to have a listen, and I noticed that your locker door is open. Likely, it is blocking the motion sensor in the switch from "seeing" you, and so it thinks no one is in the office and is turning off the light switch, beeping in the process. Additionally, your locker door is open at a ~45° angle, so likely the sound is reflecting off the locker door towards the closet door, making it sound like it's coming from there. I'm guessing you don't normally have your locker door open, so that's why you hadn't heard this before? Just my guess. John