I think most places where you have people and a load of technology and infrastructure will create a hum. I've lived in a few places which were either dark-sky areas or were very agricultural with low population density and there was definitely either less or no hum.
Recently in fact i was in rural wales, and it was very odd to not hear a hum.
Perhaps it's like light pollution, if you go up onto the hills around any city (easy in Yokshire) you'll see the orangey glow of the lights rising up, it creates a kind of orange cloud over the populated area, it's not a specific light, or even a group of lights, it's the glow from hundreds, probably thousands of small light sources.
I'd guess the Hum is the noise equivalent, we just can't see it, and to be fair, it's more disconcerting to hear something we can't see than it is to see something we can't hear.
That said, it could just be the mind-waves emanating from Menwith Hill to control us...
