The 4 speakers on top of the door represent the order of loudness of objects. The smallest speaker represents the smallest sound and as the size of the speakers increases, so does the loudness. So you need to change the white square colors to match the color of the object/animal. The order will go like this:
Top left square = Quietest = Dog sleeping = BlackTop right square = 2nd loudest = Door knocking = RedBottom left square = Loudest = Alarm clock = GreenBottom right square = 2nd quietest = Bird singing = Blue
As you do this, a key will be revealed and you can exit this level.