My computer makes a sound when switched off

Question

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.

Solution

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.

Comments

[gronostaj]

I'm afraid we can't help you. It's a random issue and we can't diagnose it without access to the hardware. You can though, just try to pinpoint the source of buzzing.

[davidgo]

Please record and upload a sample of the sound.

[SewerRat]

The noise is coming from the PSU. The "winning" is loud, at least for me since I am very sensitive to sounds like that. Should I be worried and replace the power supply or is it ok to whine?

[Mokubai]

It's normal and is a feature of pretty much every switch mode power supply to some degree. I wouldn't worry about it. Some might be quieter, some might be noisier , it all depends on component tolerances and luck of manufacturing as to whether the noise falls into an audible frequency. I'd bet that a new PSU would be similar if not the same, but you might get lucky. It won't appreciably affect the lifetime of the PSU so I'd ignore it personally.