Interesting. Yeah, it's strange that I never seemed to notice the low hum until, say, 5-6 years ago. I assumed it was the house in which I was living at the time, but we moved and I continued to notice it. In my case, both areas are kind of your "standard" suburb and not too far away from one another. BTW, I've also wondered if it was from some far-off industrial source.

But, I also know we lose our high-frequency hearing as we age. I wonder if that somehow increases our sensitivity to the low frequency range.

In any case, I'll have to try the white noise. Seems like it could help with sleep quality, which might in turn reduce sensitivity to it.