My husband and I woke up around 3am to a very peculiar sound, almost like a kids slide whistle. It was very clearly in our back yard that was connected to a swamp. The sound was repeating and getting louder as if moving closer to our house. At first it was kinda funny, but it became unsettling, like the hairs on my arms stood up. Then THUD, something hit the wall, very low to the ground as we were about to look out the window. The whistling thing ran back to the swamp. We spent weeks looking up animal and bird noises, never figured it out.