Why is there a quiet squeak and crackle from the power supply from the motherboard in the off state?

Question

Computers

Good afternoon.

Today I listened to the PC in the off state and found two sounds:

1. There is a monotonous quiet squeak from the side of the motherboard, like from a transformer or a smartphone plugged into a power supply socket. The sound is barely audible, you need to bring your ear close enough. There is a possibility that I am mistaken, and it is not the mother who squeaks, but bp. After turning off the bp toggle switch, the squeak goes away after 10 seconds.
2. If you bring your ear to the rear grille of the PSU, you can hear barely perceptible crackles. You have to listen directly.

I emphasize that the PC is turned off, but not disconnected from the network. The PC was assembled six months ago, it works flawlessly.
BP: beQuiet! Pure Power 11 400w
Mother: Asrock b450m pro4

What could it be? Problematic PSU and it needs to be changed? Or is it the norm?

Answer 1

When the computer is turned off, the power supply still works, there is a standby voltage of 5 volts, and some motherboards allow you to charge, for example, a mobile phone from USB ports on a turned off computer.
The volume of the squeak depends on the quality of the PSU components, the squeak itself is normal.

Answer 2

Because you have not de-energized the entire device, but its individual components. There is a rather tricky power management system , see G2 mode. To maintain the performance of this circuit, a little energy is needed, so it is consumed. And chokes squeak.