jmke

Many computer users have run into the issue of whining LCD monitors. Usually, it does not occur when the monitor is set to full brightness, which is usually too bright for most users. The natural response is to turn the brightness down using the monitor's controls. That's when the monitor can start to emit some high frequency tones, which are described most often as buzzing or whining. The noise usually gets worse the more the screen is dimmed. The source of the problem appears to be components in the electronic circuit which controls the brightness of the CFL bulb that lights most LCD monitors. Most likely, this is some form of PWM (pulse width modulation) circuit, a very useful tool that, alas, can have negative side effects. For example, while it allows a fan to start reliably at unusually low speed, an improperly matched PWM control circuit can cause a DC fan to emit more clicking, buzzing and chattering noise as it is slowed. A similar effect may be happening with the monitor CFL bulbs. To modify this electronic circuit in order to reduce or eliminate the whining noise is an impossible challenge for most users. Thankfully, there is a simple workaround within the software controls bundled with most video card drivers
. The color adjustment screen in the display characteristics control panel also provides a brightness setting. Using this control reduces the brightness in the video card output. This bypasses the monitor's electronic control circuit, which can be left at maximum brightness, thus eliminating the noise.

http://www.silentpcreview.com/stop_lcd_whine

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