I had that happen to me a couple times when I was at my other company.
I worked some late nights during tax season.
My desk wasn't too far from the admin area - they had their own set of equipment including individual laser printers on some of their desks.
I was sitting quietly for a good amount of time and then I heard the printer on the other side of the cubicle wall start spooling. It freaked me out in that instant, until I looked around the corner to find out what was going on.
Turns out, it occasionally would do that when not in use but was left on. I think it was just temporarily warming up and then going back to powersave mode.
