Not sure what's making the noise, but it's coming from my motherboard. A very high pitched electric whine. Any clue as to what it is? It's not the fans, none of them are spinning with the sound. It only occurs after the comps been warmed up, and continues until it cools off(even if it is shut off) The only way to get the sound to stop is to unplug it from the wall. Could this be the PSU? Not sure. Please help!

It could be the PSU or it could be the motherboard. On the motherboard you will see some coils of fairly thick copper wire wound round an iron core. These are called chokes and and help to eliminate interference. There are some in the power supply as well. If the windings is a bit lose then they can start to vibrate at a high frequency causing the whine. The noise is likely to get louder as the computer warms up and the copper expands. You can test for this if you touch them with an insulated screwdriver, the whining should stop. You can also get a similar noise front the core of transformers. As the noise stops when you pull the plug from the wall suggests that it is the power supply at fault. If you can stand the noise you can ignore it as it isn't doing and harm. Stuart

Sorry, but the last sentence of the above message is not correct.. If the fault is in the power supply. If it is the power supply whistling it is likely due to a faulty capacitor not doing its job. Far from being harmless, it indicates a fault. If the fault is occurring one the regulation control, the mother board could be damaged. One type of power supply was very fond of killing the north bridge when a capacitor failed causing the 5 volt supply to rise to 12 volts! You should check the supply by substitution to be on the safe side! Computers... designed to entertain,help with work but most of all to frustrate you!

Continuing from response 2, have you had a close look at the mother board? Check the physical condition of the electrolytic capacitors, especially around the CPU. The tops of them should be flat and silver in color. If they are swollen and/or have a brownish stain on them, they have failed. Computers... designed to entertain,help with work but most of all to frustrate you!