How come nobody mentioned about hiring a structural engineer to check out the place?
Don't always jump the gun that a place is "haunted". Make a log of what time these things happen: time, date, weather, temp and humidity levels. It's not that I don't believe in such things, but I do believe one should make proper real-world investigations first before classifying problems as "unexplained".
And yes, just open the door lah. It could very well just be a prankster.
Ockham's razor: The simplest explanation is usually the correct one.
Or leave the door open? and see what will happen?
I heard people saying that if u see scratching sound on wall or door, sometimes it is caused by 'white ants'.. so check it out.