Place a chair with a straight, high back in front of the door. It should be made of cloth, solidly built and have no gaps or decorative spaces in the back. Press it directly against the door so it covers the hole.
Purchase a piece of foam board slightly smaller than the door and place it against the door. Secure it with double-sided tape. You can write on it, paint it or hang things on it.
Hang a curtain rod over the door by screwing two boat hook brackets into the door frame -- one at each of the top corners. Position a curtain rod so each end rests of one of the boat hook brackets. Drape a thick, heavy curtain from the rod. Choose curtains that are floor length to eliminate as much noise as possible.
Set a bookshelf in front of the door with the hole. Drill the bookshelf securing mounts to the door itself, and let the bookshelf rest flush against the door.
Cut a piece of foam bed padding to the size of the door or smaller. Secure it to the door with double-sided tape to cut down on the noise.