Since moving to the Pittsburgh area (slightly north of Pitt)and more specifically about two months now, I have been hearing a very low pitched hum. It seems to be more focused in my right ear and since I haven't been working in that time and it's cold here, I've been inside most of the time and that is where I usually hear it. It is almost constant, especially when there is low noise level (preparing for sleep or just waking up or merely sitting on the couch).
It usually is described as a diesel engine but I have also described it as a propeller plane, which is how I would describe it. When I hear it I usually can tell it is pulsating (actually, right now while I am typing this the pulses have slowed down by a factor of 2-3). That's interesting. About 1 minute and 20 seconds into this clip there is a simulated hum. Mine sounds almost exactly like this. Most of the time the pulses are not spaced evenly amongst each other.
Here is another clip from Unsolved Mysteries.
My daughter's mom (my SO)and my daughter live just about a block away up a hill with her best friend. I'm over there fairly often watching my daughter (more convenient for her and school) while they are at work. I hear it over there, as well. I've tolled my SO about it, she thinks it could be my tinnitus. Tinnitus, however, is usually high pitched sounds, not extremely low.
The most well known case of this hum is Taos, New Mexico, where quite a few residents are able to hear it. Most people say it is disturbing and even debillitating. While I agree it is disturbing to me, I mean... come on... look what else I've experienced.
I will have to admit, I have heard the Hum once before. I was about 15 at the time and we had just moved to a house just outside of a small town in Missouri. There was a 15 foot conifer tree just outside my bedroom window. I heard that damn hum quite often and it sounded like it was coming from the other side of that tree. I used to think that it was possibly some kind of extraterrestrial event or that it was a military application.
Back to the present: About 3 weeks ago, I heard in my bedroom a series of sounds that sounded like photo snapshots being taken. I also heard electronic static that seemed to not only come out of the radio, but from various other locations throughout the small room. At one point, it sounded like a heard a voice say... "Leave". I called my SO and her friend to come over and check it out. Of course, at that point it had stopped as suddenly as it had started.
I can't even begin to explain what the paranoiac in me is theorizing. I do know, I live in a "basement" apt. of an old typical northeastern house, almost like a row house, just not attached to any other buildings. There are 2 apts above me. The last tenant moved out just a few days after I moved in, and there hasn't been any renters since. I've been late with the rent (not purposely) and haven' even paid December's, yet the owners haven't contacted me. Humph.
The "snapshots" I was hearing (if it was projected by an outside source) may be explained by a microwave auditory effect. From Wikipedia "The clicks are generated directly inside the human head without the need of any receiving electronic device."