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When my PC is turned off and I bring my head very close to the PSU, I hear a high frequency noise. Is that normal? I can't hear when I am like 2 metres away from it. And it's only there when turned off. My ethernet port blinks so the pc is using some power even through it's off.

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The most common cause of high-pitch audible noise is something loosely known as coil noise. Specifically, it's a vibrating toroidal inductor. As you can see in the picture below, they commonly apply glue at the factory to dampen the vibration. It is harmless to the electronics, but annoying to people and animals.

To answer your question, it's not "normal", just a common flaw. Personally, I find such noises unbearable, and a sign of poor manufacturing. If the computer is under warranty, I would ask for the power supply to be replaced. If it's not under warranty, and it uses a standard form factor, I would replace it with something that has met the criteria for 80 PLUS certification.

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High frequency noise coming from a power supply usually comes from a leaking capacitor. It may not be an immediate issue, but it probably won't get better. You can Google for the sound and descriptions of the problem. Most people live with it unless it really bothers, then they replace the PSU.

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  • Couldn't it be from the coil? Is it surely a faulty PSU or perhaps it's normal to do it with a low load? People have told me that on low load the frequency could be low enough to be auidble(below 20Khz) while on higher load it's not.(When my PC is off, my USB ports still work - are powered that is, my Ethernet as well as my keyboard). Will I get a replacement just because of that noise? Also the voltages reported in the bios seem pretty normal.(perhaps I will post them later). – Ivan Jul 19 '14 at 19:53
  • Sure, could be the coil, but bad caps seem to be common. Both are sources of squealing noise. Either way, if you can locate it to the PSU, replace it. Most PSU's are not user serviceable. – Blackbeagle Aug 21 '14 at 19:25

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