EDIT: Jen has confirmed the sound is NOT teeth grinding. This makes sense because towards the end, when your sanity is all but depleted, the sound becomes greatly exaggerated and magnified.
Original message before Edit:When Daniel is placed in the darkness, and his sanity begins to decrease, the insensity and frequency of the teeth grinding noise really becomes unnerving. This alone is unsettling, although I found the noise to be extremly exaggerated.
Anyone else find it unnerving as well?