This one could be a machine or perhaps sound reflected from a distant factory, but the fact that, despite its softness, the witness claims that it hurts his ears is unusual.
I could only listen to this briefly. Don't know if it's the pitch, frequency,or whatever, but I found myself clenching my jaws and experiencing general discomfort in my head, but not like a headache. It may not be anything more than some of kind of human made machinery, but it IS annoying, whatever it is!
I made it about halfway through before I had to turn it off. I too experienced the discomfort in my head, but I also started to feel very uncomfortable in my whole body. I could hardly be still and I felt as though I wanted to run away. The sound (not the feeling) also reminded me of a subliminal healing tape I had a long time ago, which makes me wonder if these sounds could possibly be some sort of subliminal message.
OK...Just did my own little experiment. This sound did remind me of a Theta wave meditation that I use every now and then. It is quite relaxing, unlike this pulsing sound. My boyfriend happened to be dozing on the sofa just now. He has not listened to any of this vid or my Brainsyn meditations. While he was sleeping, I played 4 different Branisync meditations for a few moments a piece. He continued sleeping. I went to this vid (and covered my own ears!) within seconds he started moving around, opened his eyes, and asked, "Is that the sound you were telling me about? It's making me feel nauseous."