Monitor 1084S-D1

[JimS]

The flyback transformer is used to generate the high voltage needed for the CRT. It's driven off the horizontal sweep that moves the beam across the screen. Using the sweep frequency - 15kHz - instead of "mains" 50/60 hz means the transformer needs less iron. But it also means that if something is mechanically loose in there, it can vibrate at 15kHz and be annoying to those who can still hear that high. ;-)

I've seen a lot of 1084's flybacks actually break their soldered connections to the main board....
Take it to a tv shop if it's a problem.

[JimS]

That's impossible to say. The noise isn't a sign of impending failure, just a side effect of the frequencies used in there. It can fail without making a noise, or can whistle like a teapot for years.