My computer makes a sound when switched off

audiomotherboard

I have recently build a new computer and every time the system is switched off there is a silent buzzing sound coming sound from my pc. Couldn't locate the exact source of sound but I am pretty sure it is not a PSU issue as I plugged a different one into the system and it does the same sound. I suspect the motherboard is making the sound, but I want to be sure before sending it back.

Best Answer

The noise is probably coming from your PSU.

Your computer is not truly "switched off" when it is shut down.

As a result there are a couple of low power lines that are always on. Specifically the "5v_standby" which is used to keep an amount of devices operational so that your computer can wake itself up. This would include timers, so that it can wake up on a schedule, or networks so it can support Wake-on-LAN.

What this means is that your power supply can not truly switch off either. This means that there is always some small amount of conversion from mains down to low voltages required.

Chances are what you are hearing is the few small switch mode power supplies inductors "coil whine". This noise will always be there in your computer, but with the main CPU and components turned off the fans will stop and the computer is actually quiet enough for you to hear it.

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