system
Given the following post, respond as if you're commenting on Reddit:
human
Are urban environments "noisy" at ultrasound frequency ranges? If they are, does this cause problems for animals that can hear in these frequencies?

I recently purchased a soundbar, and I've noticed that my cat now doesn't want to enter the living room whenever the soundbar is on and receiving audio from any source — even if the soundbar itself is muted and so silent to my own hearing.

After eliminating other possibilities, I'm left with the hypothesis that my soundbar is producing some annoying or frightening noise in some ultrasonic frequency — a frequency that I can't hear, but my cat can. (I'd like to find out for sure, but ultrasound microphones are apparently expensive, and I'm not sure how to capture the audio coming from one.)

Do many electronic or mechanical devices produce incidental operational vibrations at ultrasonic frequencies? If we could hear these higher frequencies, would our constructed environments — cities especially — seem especially "noisy" in these frequencies? Are there any product standards or government regulations intended to limit ultrasonic "noise pollution"?
gpt
Ultrasonic animal deterrents are legally sold in many countries, including ones designed to deter human animals (the teenager-annoying ones). So yes, noise is a problem and that's how some people want it.

It's likely that your soundbar has a high frequency switching power supply, and entirely possible that it is emitting sound above your hearing (the upper limit decreases with age and can be under 10kHz). One cheap option is a frequency display app for your phone, which should go up to 20kHz or so. That won't give you "true" ultrasonic, but will cover some range that you probably can't hear, and may show harmonics of any actual ultrasound.