As someone who experiences this phenomena, but whose family denied its existence, I was delighted to find out that it has at last been recorded. More info and a link to the recording: http://www.atmayogi.com/?q=node/55

The annnoying thing is that there is still no explanation for it. The New Zealand scientists who recorded it seem to put it down to wind blowing over adjacent sand dunes - which merely illustrates that they are cocooned in their own world and don't have a global perspective. This is a phenomena that has been going for many years. Like many other people - apparently - I first became aware of it in the 1990's. If indeed it first started at that time then that would seem to rule out most natural phenomena such a geothermal or tectonic activity, wind over sand dunes(!), tidal activity etc. And since I live just about as far away from the sea as you can get - in the UK - I'm happy to promote a sceptical view fo these last two explanations.

But if we rule out natural phenomena, then I'd guess that its most likely to do with the low frequency signals used to communicate with submarines, or else something to do with the massive increase in use of mobile phones. I doubt whether it is simply a general increase in the background Electro Magnetic(EM) noise of our gadget ridden world ... but who knows.

I haven't been as aware of the noise during the summer, but I am again now. But there again, perhaps I'm just getting used to it, or maybe age is dulling my extra sensitive hearing (both high and low frequencies, since you asked - which is a bit of a bugger for other reasons that I'll not go into just now).

Any other sufferers (some call us "hummers" apparntly) around here?

If I wake in the wee small hours it would be nice not to listen to the distant runbling of a diesel engine on tickover; it was very comforting to find out that other "sufferers" descibe it in exactly the same way that I have done to my disbelieving family.