My computer currently makes a constant sound when it is turned off. The kind of sound you sometimes hear from a television for example. A really annoying sound.

Could anyone point me in the right direction on what causes this sound? Some time before this sound started, my computer stopped working all together, which is still the case at this moment.

When I currently start my computer the following happens:

  • The coolers are running
  • The hard drives are running
  • The computer makes a constant sound of the coolers, it isn't going faster or slower
  • Nothing appears on the screen
  • CD/DVD-roms aren't opening

My money's on a bad power supply.

Power supplies are transformers, and they can make a very high pitched (I hear it as almost a hissing sound) noise, especially when they are failing/failed. In this case, it sounds like the power supply has given up the ghost and now makes noise, as you say, 'like a TV set'.

As to why this happens, I have no idea. I suppose this could be oscillation of a hardware component, or something. One message board says this about televisions:

As CRT TV's get older, the laminations in the coils get dryer and looser. allowing the coils to vibrate. This acts as an acoustic amplifier for subharmonics of the frequency the circuit that the coil is in operates at."

But I have heard the same noise on computers and very shortly thereafter, they are dead.


Is this a High pitched whine or squeal ?

It's probably coming from the power supply.

Does your power switch do anything ? If it does, then it's most likely the power supply.

I'd suspect either

1) your PC power supply is not working
2) you motherboard/NIC is broken.

If you're confident to open your PC, Unplug it from the power lead, Open your PC and unplug the power supply from everything. (motherboard, drives etc)

then plug the mains power lead back into the power supply. If the noise is there, it's definitely your PC power supply whining.

If you have or can borrow a voltmeter/multimeter, measure the voltage on a power supply to hard drive connector. ( The old ones are easier than SATA ones to use for this). Voltages are DC, up to 20 volts. The voltages present normally are not dangerous, but take care not to short the power output leads together. As your fans and HDD's spin up, the voltages must be almost right.

From the RED to black wire(s) there should be 5.0Volts. Tolerance is around +/- 5% so max 5.25 min 4.75 From the Yellow to black wires there should be 12.0 volts. As low as 11.5 volts in fairly normal. Over 12.5 is abnormal. The connector to the motherboard carries other voltages, but testing 5.0 and 12.0 is a very important (easy) first start. The measured Voltage pulsing up and down is bad. Steady voltages are good. The ORANGE wires on the motherboard connector carry 3.3Volts : they are critical.

If the power supply looks okay, it may be the motherboard. If you've got a spare (old) computer or know someone with a spare junk PC, you might try swapping your power supply into the junk PC. If the junk PC boots, then it's probably your motherboard, if it doesn't it's probably your power supply. If the power supply has wrecked a junk PC (which seems unlikely, given your drives and fans run okay), well, that's not too bad.

Beyond this it is time for someone with a background in computer repair.

The hissing sound is normally the power supply being overloaded. The standby power supply is hissing ( when the PC is off). The most likely reason is that the large (electrolytic) capacitors inside the power supply have dried up and are not storing enough power as the mains voltages oscillates ( it's alternating current), so the power supply struggles and the transformer coils ring ( that hissing sound). Poorly varnished or loosely wound transformers will hiss from new, when not overloaded. Old TVs get this way for similar reasons.

  • Thank you for the very clear explanation. I will look at your suggestions as soon as I'm at my PC. – user23630 Jan 5 '10 at 13:45

Where is the origin of the sound? If it's through the speakers, yes, could be interference.

If it's not, it could well be the power supply. They can emit a high-pitched whine when they're dead/dying.

Check your graphics card. If your card is fried, the machine may not post.


Number one reason for random sounds is interference.

Without knowing the problem of your machine, it is really hard to know if it related.


Or, is your mic gain set to very high and you have a feedback loop?

Is you mic obstructed in any way?

  • 1
    Unlikely as it happens when the laptop is turned off. – Connor W Jan 4 '10 at 22:03

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