Ultrasonic Waves Are Everywhere. Can You Hear Them?
By Rafi Letzter, Staff Writer | May 10, 2018 04:15pm ET
There are horrible sounds all around us only a small group of people can hear. They almost always come from machines — sometimes intentionally, and sometimes by accident. They're loud enough to be annoying and cause headaches in people sensitive to them, though it seems they aren't usually loud enough to cause permanent health issues. And scientists have no firm idea of how common these sounds are or how much damage, if any, they're doing to society.
https://www.livescience.com/62533-ultrasonic-ultrasound-health-hearing-tinnitus.html
