I've heard it almost all the time since i moved into my new house four years ago this July. At first I thought it was a generator being used on the building site but now know it wasn't. The hum is only inside the house and disappears when I open the doors / windows. Environmental health - noise pollution cannot help as they cannot pick up low frequency sounds on their equipment! I have just had to learn to live with it. I wear ear plugs at night but they only make it sound a little fainter. I can still feel the vibration. Sometimes we just have to sleep out to get a good nights sleep. Any ideas to help will be greatfully appreciated!