A timely article:

http://www.livescience.com/38427-the...-taos-hum.html

I've been hearing a spectral Hum just since this Spring. It sounds like distant thunder. Just yesterday I went to a weather channel to see if there were storms anywhere. Not at all. The first I noticed it was that nasty weekend we had spate of tornados, one which ploughed down a strip through Moore, OK.

That weekend at the pool I asked my daughter if she heard it. No, know one else did either. Since then I've been hearing it fairly frequently. I marked it up to a heightened sensitivity due to allowing my Mini Cooper to get some hail damage. That weekend there were in fact storms in the area. Though, when I heard the 'thunder' they were a few hundred miles away.

I'm in the right age group for experiencing this phenomenon, but it doesn't bother me, at least yet.