I’d guess it’s on all MKIIs. I have two OTs. Both bought brand new. Both have the same exact sound. I’d also guess that some people cannot hear the frequency at all.
It is caused by the screen.
I keep brightness on low as a matter of preference, so the sound is very faint.
I’ve looked before and I can never find any info about OLEDs actually making noise, I knowthey can induce a lot of hum and whine in audio signals but nobody seems to say anything about them mechanically making any sounds, other than coil hum in OLED TV sets. But this thread and a few other things I’ve seen make me think that they can.
I had to return my MkII recently because of erratic encoder and button behaviours. They returned it very quickly with a replaced UI PCB, which has resolved the behaviour. However, I have since noticed a high-pitched whine coming from inside the unit that I’ve never heard before. I thought it’d be affected by the brightness setting, since I’ve had this with similar devices before, but there is no change to the noise whatever the setting. It’s quite irritating when I need a moment to think in silence. I emailed support a couple of weeks ago. No reply as yet.