High Levels of High-frequency Noise in Public Spaces

I can attest to the fact that such sounds exist. I was one of those oddballs in the days of my youth, being able to hear well into that range. Motion detectors drove me crazy. There were certain stores that had something, I never figured out what, that drove me out of there in a hurry. The aging process has removed that ability, although when audio tested, my better hearing is still above 6K Hz, with a definite dip in the lower ranges.

The same with me when I was young; I could easily hear the 15,750 Hz television flyback frequency, and many large stores had something somewhat above that frequency running all of the time. I asked what it was, and I was told that it had to do with sensing motion when the store was closed. When I asked why they didn't turn it off during business hours, they told me that I couldn't possibly hear it.

I avoided those stores.

Couldn't hear it?? Oh yeah we could. I know what my cats must feel like when I run my DCC controlled trains. There is another source of noise just above the normal human audio range to add to the noise pollution list. It is somewhere around 30KHz, and has been noted in application documents that the motor does "hum" at that frequency, so I assume my cats can hear it.

I know I went past 20KHz, as my buddies tested me in an EE lab one day, without my prior knowledge, with 20KHz tone and I reacted to it appropriately. Convinced them at that point. I know what I heard in stores was above that.