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.
PSU Noise when turned off
hardware-failurenoisepower supply
Related Solutions
You're right, try to find that manual and reset the BIOS. Before that, you could try to hit Esc to stop any memory test, to maybe allow you to get into the BIOS setup after all. But I assume you've tried that as well.
If you ever get into the BIOS again, you'll probably find some screen that shows the current fan speeds. If none claims to be zero, then maybe the BIOS did not find a faulty fan after all, and this is just some bug, like responding to some fans that are not present at all. I think you cannot be sure that a fan in the PSU is indeed not working at all. Save the money for a new PSU; first try to get your computer to boot again!
If you find that manual, then maybe you can also find connectors on your motherboard for additional fans. If you cannot reset the BIOS (which, however, should be possible I guess), then attaching a fan to any non-used connectors may help your computer boot. You could also make sure that the attached fans are actually connected using all pins on the connector. (To measure the actual speed some feedback is required, which I assume needs more than just two wires for the power source.)
I actually doubted the BIOS would know the speed of any fan inside the PSU. But I stand corrected: a comment from Nikhil states that a PSU may be connected to the motherboard to tell it about the fan speed (and temperature?).
EDIT 2: I happened to see a link to How to Reset Your BIOS at Overclocked too far - computer will not boot here on SU.
Typically that noise happens when computer and speakers have different ground levels, explained here. Are you sure that you did not also change anything in that regard, different outlets, etc? Is your pc connected to other devices, antennas, network switches, etc? Try connecting your speakers and computer at the same power outlet, with an extension cord.
edit:
- When I disconnect the audio cable from the speakers, there's no noise.
- When I connect the audio cable to the speakers only (not to the computer), they are very noisy.
very odd behavior, looks like there is something wrong with the cable or the speaker system itself. Is it a hissing noise or a deep hum?
Best Answer
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.