Looking for some scary "music" for Halloween, yet don't want your average screams, creaks, and howls?
Then check out the Conet Project. I heard about it a few years ago while listening to NPR. The short version of the story is just as eerie as the audio tracks: some guy discovered number stations being broadcast over short wave radio. These number stations typically broadcast some sort of simple lullaby or popular old tune followed by an array of numbers being read by (typically) a female voice. They are believed to have originated in the cold war, and are coded messages that are transmitting some sort of instructions. Think "the cow crows at midnight", or "the red boot shines when lit"...total nonsense to us, but it means something to someone (i.e. shoot that one dude).
If that's not creepy enough, then imagine finding these short wave signals being broadcast years later, without any sort of explainable source. The founder of the Conet Project has looked, and has had no luck. Some theorize that abandoned computers are sending them out. Others suggest there's some random guy holed up in an underground cave, still believing a nuclear winter is about to hit at any moment and doing his best to keep his spies informed. Whatever the case, these signals are not traceable...nobody knows where they're coming from.
They're broadcast in all sorts of styles and languages. Make sure to listen to a few samples online. And then get ready to really creep out the neighborhood kids...and yourself.