Wow, I love spooky sounds. What an awesome soundtrack for a movie!

I work with giant industrial machinery and I've heard machines make noises almost identical to this one. Piston/rod/cylinder assemblies are very common in large machines, I've seen them as big as 9 feet in diameter. Sometimes when the piston moves in the cylinder it sets up a vibration and they act like a giant horn and you get a really spooky sound like this one. So that's my guess. It's a giant saxophone.