I think that the Janitor Pops is the one doing the haunting. The reason I think it is Pops is because he doesn't want the theater to close/shutdown.
I also think that it was Pops who was behind the mask.
I think that some of the noises are coming from the pigeons, the circular stairs, the air vents, and air pipes.
I also wonder if we're ever going to see Ms. Gewertz. I don't think so.
On my water xylophone I played 'Twinkle, Twinkle, Little Star.' It came out really clear and in tune.