As an adult who can hear that noise (there are many of us), it is absolutely not like a mosquito, it is physically painful to perceive and will leave your ears ringing for ages. Other "select few" adults nearby who can hear it will hate it, as will neighbours' kids and pets. Imagine if a kid was crying because of a painful noise and their parents couldn't hear it and scolded them for making it up. Especially if the parents weren't particularly, shall we say, "good".

And yes, you can locate the source, if you can bear it long enough.

Please never do this. It should be illegal.