Try using something from Raison D'Etre! While they are not the easiest band to find their pieces run 20 minutes plus or another great band is Lustmord.
It is mostly low key noise but it is very moody and works in a pit of hell scene or if you just want to creep people out both of these groups work well. Lustmord is more for the hell bit but the Raison D'Etre is more eerie atmospheric music with human synthesized voices in the background. Pretty wild stuff and well worth checking out. If you go to the Cold Meat Industry record label website you will find samples of the band. I have included the link here see if this would work, these are only excerpts of some of their longer tracks:
http://www.coldmeat.se/home.html
You may have to locate the band Raison D'Etre and then it will take you to a full page of sample downloads. They are dark and moody and a lot of fun. Spooky minimal music that can certainly scare the TOT's depending on your scene, even in professional haunts it works great to play outside while people are waiting. Usually I mix in other Halloween sounds into this as well which really helps to freak people out.