When I was a kid it was popular for people to have records playing (yes, LPs) of weird sounds out their windows. Screams, moans, creaky doors, all those cheesy sounds. One house had whale songs playing, which I thought was cool and not at all scary.
I was thinking about this today, and suddenly remembered a post I put up last July about extremely creepy sounds from Saturn and the Earth's aurora. Wanna scare the kiddies on Halloween? Download those and loop 'em. You'll probably scare them enough to have lots of leftover candy.
Oh, and the picture above? That's just a little Halloween gift from the Chandra space observatory.