LOL same thing at my old job! We kept hearing weird flapping sounds in the drop ceiling. Freaked us out for weeks until a maintenance guy found a nest of pigeons had gotten in through a vent. So much for our office poltergeist.
Furry squatter above the tiles" is the perfect way to put it. I used to be fully convinced our office ghost was some creepy paranormal thing, but nope, it's always just an animal.
Know that feeling all too well... our old warehouse had constant scratching sounds that kept everyone on edge. Turned out to be a family of raccoons in the attic. So much for our exciting ghost stories.