Industrial sounding noise in the air

[owlwise]

I live in Upper Sydenham, off Westwood Hill, and have noticed in the past few days a continuous heavy droning industrial type of sound in the distance that is disturbing the quietness I usually experience if I'm outside in my garden. I've gone out there at night and still can hear it.

Can anyone else hear it? Does anyone know what's causing it?

[Parker1970]

I have sometimes late at night if its too warm and open my bedroom window, that I hear a "buzzing" sound, higher pitch... and it goes off after a while. Never figured out what it is, but it is distant but then I live at Cobbs Corner at the bottom of westwood hill. Could be the same thing?