Philips Monitors Make an Annoying Sound
Both speakers make a loud noise at around 20kHz. Many older people will never hear it, but if you can it will be the most annoying experience ever. The noise is not constant, it happens when there is something bright on screen, such as a website with the white background. It is so high pitch that sometimes you may not even consciously realize it is there.
I have tested with a sound spectrometer, and it is clear the noise comes from the monitor, at a fixed frequency and it depends on the brightness of what is on display. Educated guess, there is some PWM circuit that controls brightness and that resonates. I have checked on colleagues screens and the same happens sometimes with frequencies as low as 12kHz, just that they couldn't hear it.
I had to return the screens, there is no way around.