Not seeing anything of particular interest on the second floor, you decide to press on to the third. Unfortunately, upon reaching the top of that set of stairs you find another unremarkable hallway filled with rows of doors. No additional stairway presents itself this time, leaving you with only the hallway stretching left and right to further explore. The only thing which distinguishes the two directions is a ladder leading up into the ceiling at the left end, and a window at the right end which presumably looks out over the grounds.
Before you can decide which direction you want to head off in, a scratching noise reaches your ears, seemingly coming from a door toward the right end of the hall.