I had never heard of this before but for quite some time I have experienced hearing a sound, late at night that is like a generator hum, droning away in the background. I have had my ear to all our electrical appliances, I have been outside front and back and it doesn't change - it is just 'there'. Firstly, I blamed it on the hospital generators/ air conditioning as the hospital is across from us but when I 'followed' the sound it didn't get louder or less. Some nights I don't hear it. Last night it was very loud and everywhere - so much so that I had to turn on the fan in our bedroom because I was concentrating on listening to it rather than reading and going to sleep. One night last week I decided to put a few words into Google and was really surprised to find out that it is a common phenomenon (if you are sure you do not have tinnitus). I thought it was perhaps some mechanical work going on in our area. I have been pondering on the topic ever since. Lots of people, I think one article said 2 in 10 experience this low frequency sound. One woman moved house and could hear it all the time until she got to the end of her road. My O/H thinks it is probably the hospital but I am not convinced - he doesn't hear it and he is well known for listing my 'super-powers' such as my sense of smell - his sense of smell is not very good at all (another story), so he thinks my hearing is super sensitive! I wonder, does this affect anyone on here?