So we've been hearing this mystery sound in our house. It can only be heard in three rooms. The master bed and bath (which take up 1/3rd side of the house) and another of the rooms on the other end of the house. It's like a constant running motor sound. It's at all hours, and makes no sense. You can't hear it downstairs, only upstairs. There's no device inside or outside that we can fathom it could be. So I thought I'd see if anyone had any ideas WTF it could be...
We have old pipes in our house and sometimes when the water heater is going the pipes upstairs sound like a motor boat revving up. Usually it just lasts for a few seconds though, not a sustained noise like that.
Do you have well- or city-water? You might be hearing the water pump in the house if you have well water... or if it's city water you might be hearing a "pressure booster" running. If your heat is running it could be related to that, maybe a ventilator or exhaust fan. All sorts of things. Heck you could just be going stark raving bonkers. Happened to me and I was much better for it.
This is exactly what I hear every now and then at night, and I'm very sure it's not a car, nor something coming from inside the house. It's either an inner ear problem, or "The Hum" (whatever that may be) just glad to read I'm not the only one to hear it!