Thanks for sharing this. There could be all kinds of scientific explanations, but I like the idea that there is too much energy in the developed countries that fogs our senses. I often hear a deep hum late at night, which is most certainly caused by a pump running somehwere in the neighborhood. It almost drove me crazy for a while, but then I decided to simply ignore it. I can still hear it, but it does not bother me anymore. In other words, I delibertately decided to dumb down a bit.