Interesting. Sometimes I think I can hear something, other times not - not that I'm actively listening for it. I have tinnitus though, so maybe that distracts me a bit.
It's certainly not a new phenomenon. From the little I've heard, people all over the world experience something similar. It seems to be Wrstern/city living issue; probably comes from living in a world of electrical fields, devices, power generation etc?
It can become very distressing for some people.