Definition
Coil whine is a physical phenomenon in which a power component inside an electronic device vibrates slightly when a sudden surge of current flows through it, producing a piercing, high-frequency noise (a buzz or a squeal). It happens most often when a device draws a lot of power, such as a high-end graphics card or a power supply.
Why do you hear a buzz when you run a demanding game?
When you turn on a garden hose and the water only trickles out, it stays quiet. Open it suddenly at full pressure, and the hose shudders and makes noise. Computer parts work in a very similar way.
When a computer runs a heavy game or 3D graphics work, the graphics card and power components pull a huge amount of electricity from one split second to the next. That strong current flows through the inductor (coil), a small cylindrical part that keeps the voltage steady.
When current flows, a strong magnetic field forms around the coil for an instant. Because of that magnetic force, the coil and the parts inside it vibrate slightly, thousands to about ten thousand times per second, shaking the air, and that shaking reaches our ears as a sharp, high-pitched noise.
The sound is especially loud when the workload suddenly surges, such as the moment a graphics card is producing hundreds of frames per second.
A bit more precisely: component vibration and magnetostriction
In electromagnetism, current flowing through a wire creates a magnetic field around it, and a wire carrying current inside a magnetic field feels a force. A computer's power circuitry switches electricity on and off hundreds of thousands of times per second to hold the steady voltage its parts need. The switching itself is too fast to hear, but the rhythm of the current rising and falling with the game's workload creates vibrations at frequencies your ears can pick up.
These sharp current changes, swinging back and forth, make not only the coil but also nearby magnetic parts stretch and shrink by tiny amounts. In physics, this effect, where a magnetic material changes shape in response to a magnetic field, is called magnetostriction.
In the end, it's the electromagnetic force inside the parts physically shaking the magnetic material. It's a natural law of physics, so even when manufacturers glue the parts down firmly, it's hard to get rid of the noise 100% when a lot of power is flowing.
Even the priciest, newest flagship graphics card can always develop coil whine if it draws a lot of power.
Is it broken? Practical tips for quieting it
When a brand-new, expensive computer starts making an irritating buzz, it's easy to panic. But coil whine is not a functional defect that breaks the part or shortens its life. It's just natural physical noise caused by the laws of electromagnetism inside the device.
If the sound still bothers you, software settings can easily reduce it. The most effective approach is to cap the frames per second (frame rate) in the game settings to match your monitor's refresh rate, or to turn on V-Sync.
When frames are kept from shooting up into the hundreds for no reason, the graphics card doesn't pull power excessively, and the vibration and noise drop a lot.
On the hardware side, swapping the power supply for a different model sometimes changes the sound. That's because the vibration can get louder or quieter depending on how the parts are combined.
Common misconceptions
A part that makes coil whine is defective or about to fail.
It's a natural effect: a sudden flow of current makes the part physically vibrate. It's annoying to hear, but it usually doesn't affect the device's performance or lifespan.
Where you meet it
On the menu screen of a demanding 3D game, when the frame rate shoots up to hundreds of FPS, the buzzing inside the computer gets louder.
Plug an ultra-fast smartphone charger into an outlet and hold it close to your ear in a quiet room, and you can hear a faint squeal.
In one sentence
Coil whine is a high-pitched noise made when a coil inside a power-hungry part vibrates slightly from electromagnetic force.