We live in woodland. I often hear a sound from behind the house almost exactly like a creaky door opening - not a high-pitched squeaky gate-hinge sound, more like the sound made by the door of the spooky haunted house when the hapless teens are about to go in, but probably less than 2 seconds in length. I hear this sound during both the night and day, and when I do, it's just once, never repeated. Could this be a bird, and if so, what kind? Thanks!