After long thoughts on the matter, and this being one of those eternity discussions for most, I just wanted to share what I found works very well in my games (I actually have players complain when I don't use background ambient music).
I use a portable bluetooth speaker and play a mix of dark ambient music from my phone, allowing me to use it to build up eeriness.
Bands/Albums I use:
- Lustmord
- Inade
- Sleep Research Facilty
- NIN - Ghosts
- Wychdoktor
- iVardensphere (very sparingly)
- Yen pox
- Visions
- Svartsinn
- SM
- Proton Kinoun
- Phobium
Rules I have:
- No strong melody
- No singing
- Ambient sounds