Question about Dell UltraSharp U2725QE

I did buy a refurbished monitor this week, and coil whine was present. The loudest is when the screen's brightness is below 20%, which is normal in the evening when it gets dark. Most likely, it comes from the power source.

My setup was a MacBook Air M4 connected via Thunderbolt 4 to the monitor.

I have now been using the monitor for a week and am completely satisfied. I have not noticed any coil beeping either in operation or in standby.

Thank you, I bought the monitor a few days ago and there was NO coil beeping right from the start. Everything was fine for me.