Gauging the emotional response to certain sounds is one of those immeasurable things, a bit like trying to measure how the colour blue makes you feel, but I think there are some approaches in sound design that generally achieve the same effect across the board (particularly when it comes to horror).
For example high pitched, jarring sounds like squealing, scraping metal would usually denote tension or a sense of unease. With a fast attack and in conjunction with a sudden visual event this kind of sound is also very good for the classic scare. Film seems to have created it's own sound language in that where you have drawn out period of tension or building quiet, you know that the scare is coming and so creating the anticipation is just as important as the hit itself in my opinion.
If you're into further reading, someone did an actual medical paper titled "The Psychoacoustics of a Chilling Sound" where they investigated why the sound of fingernails being dragged across a chalkboard was generally deemed as being so horrible. They drew similarities between the frequencies of that sound and the alarm calls of a certain monkey, so maybe our responses to certain sounds are an inbuilt, primal thing. Can't remember the author's name :-/
Similarly, the University of Salford in the UK did a survey called "Bad Vibes" where people voted on the worst sounds online and via a booth in one Manchesters museums. If I remember rightly number one ended up being the sound of someone being sick but for some reason I find that hilarious haha.
Anyways, I'm going off topic. Subby hits, rumbles and drones are also often used to create a feeling of dread and fear. My little theory is that this stems back to a natural response to earthquakes, tornado's etc and as such can also be used to depict the magnitude of a situation (think Inception brass).
For your particular situation, I'm thinking a reversed high-pitched thing with a bit of a pitch bend just to reflect that somethings not right. The peaks of the reverse could possibly sync with the movement of the shadows? Maybe also whispers that have been reversed, reverbed and then reversed back again. But that's just me :)
+1 to the devil's chord!