When I was a child I could always hear a high pitched whine from nearby CRTs that adults couldn't. I'd always assumed that to be a mechanical effect due to the varying magnetic fields, but perhaps this was the mechanism?
The reason you remember adults not hearing it is because there is a well-documented loss of high-frequency hearing as people age.
(Which has even been “weaponised” before; there were stories some years ago about stores blasting high-frequency noise outside to deter loitering teenagers without affecting desirable adult shoppers)
Yeah, they should only work for teenagers. Except for when you are visually impaired like me. I'm almost 35 now and still hear those high frequency noise. It is extremely annoying and even borderline painful. Last year I even got the cops involved when a parked car in front of my apartment constantly emitted a high frequency noise for deterring stone marten and I didn't know who the car belonged to. It was a pretty funny interaction in the end because none of the parties involved (except for me) could even hear the noise. But the car owner admitted they had such a device installed. Resulting in them just moving their car.
It's a distribution. Probably a normal distribution, but I don't know that for certain.
Even a properly working CRT TV had the very high pitch whine. Any kid from the 80s or I guess 90s and back knows of the CRT whine. I recall it so high it's almost like it's in your head as imaginary or you could "taste" it in your 1970s/80s mercury amalgam fillings (maybe that was just me).
You lose that ability of your hearing pretty early in life or early teens (loud music damage?) but it couldn't be more than 20KHz the highest pitch of sounds that humans can hear.
The odd thing is I don't remember hearing it much as a kid in the 90's, which is why I associate it with the age/condition of the equipment. These days, every CRT I bring home is the bane of my son's existence if he is in the shop with me, but I can't hear a thing (due to the age of my equipment)
My first job also involved a dec vt240 with the same features - really badly burnt-in display and horrific coil whine that made me go home with a migraine at least twice that I remember.
It makes much more sense when you realise that the 16kHz or so frequency is well out of range for anyone over 40. Many things related to noise make sense once you realise all older people are near deaf, compared to the hearing of a 10 year old.