Dunno if this has been a topic before, I heard about it on the News the other night. The strange thing is, until I saw it on the News I thought it was just me :1orglaugh I've heard 'the hum' about 2/3am some mornings, like a very distant drone that you have to really concentrate on to hear.......its weird!
http://news.bbc.co.uk/2/hi/uk_news/8056284.stm
http://news.bbc.co.uk/2/hi/uk_news/8056284.stm