High pitched whine or squeal from monitor with no other symptoms
Sometimes this is continuous. In other cases, it comes and goes almost as though there is an intelligence at work attempting to drive you crazy. All the more so since a technician may not even be able to hear what you are complaining about if their hearing is not as sharp at high frequencies as yours. Even high resolution computer monitors running at high horizontal scan rates (beyond human hearing) can have these problems due to the switching power supplies as well as subharmonics of the horizontal scan rate exciting mechanical resonances in the magnetic components or even a portion of the sheetmetal used for shielding if in close proximity to a magnetic component.
If it is a new monitor and you think the sounds will drive you insane, returning it for a refund or replacement may be best alternative. However, you may get used to it in time.
Note: if the whine only occurs when the monitor is unplugged from the computer or the computer is turned off, this is probably normal. Without valid sync signals the monitor defaults to a horizontal rate which is within the audible range (less than 20 kHz). Any vibrating components will be readily heard. It is usually not a sign of impending failure.
In most cases, this sound, while annoying, does not indicate an impending failure (at least not to the monitor - perhaps to your mental health) or signify anything about the expected reliability of the unit though this is not always the case. Intermittent or poor connections in the deflection or power supply subsystems can also result in similar sounds. However, it is more likely that some part is just vibrating in response to a high frequency electric current.
There are several parts inside the monitor that can potentially make this noise - the horizontal flyback transformer and to a lesser extent, the deflection yoke and associated geometry correction coils would be my first candidates. In addition, transformers or chokes in the switching power supply if this is distinct from the horizontal deflection circuitry.
You have several options before resorting to a 12 pound hammer:
* Confirm that the horizontal scan rate being used by the video card is well within the range supported by the monitor. If it isn't, change it to be a one that is - in addition to possible whining, this is stressful on the deflection and power supply and may result in an expensive repair in a very short time. Even if the scan rate is supposed to be fine, changing it slightly (e.g., 5 percent) might help just because it shifts the deflection frequency away from a mechanical resonance. However, this may not be a long term solution.
* As much as you would like to dunk the monitor in sound deadening insulation, this should be avoided as it will interfere with with proper cooling. However, the interior of the computer desk/cabinet can be lined with a non-flammable sound absorbing material, perhaps acoustic ceiling tiles. Hopefully, not a lot of sound energy is coming from the front of the monitor.
* Move the monitor out of a corner if that is where it is located - the corner will focus sound energy into the room.
* Anything soft like carpeting, drapes, etc. will do a good job of absorbing sound energy in this band. Here is your justification for purchasing those antique Persian rugs you always wanted for your computer room :-).
If you are desperate and want to check the inside of the monitor:
* Using appropriate safety precautions, you can try prodding the various suspect parts (flyback, deflection yoke, other transformers, ferrite beads) with an insulated tool such as a dry wooden stick. Listen through a cardboard tube to try to localizing the source. If the sounds changes, you know what part to go after. Sometimes a replacement flyback will cure the problem unless it is a design flaw. You do not want to replace the yoke as convergence and other adjustments would need to be performed. Other transformers can be replaced.
* Sometimes, tightening some mounting screws or wedging a toothpick between the core and the mounting or coils will help. Coating the offending part with sealer suitable for electronic equipment may quiet it down but too much may lead to overheating. A dab of hot-melt glue or RTV silicone may help. Even replacement is no guarantee as the new part may be worse. For yoke noise, see the section: Reducing/eliminating yoke noise.
* A few monitors have internal cooling fans. The whine may be due to worn or dry bearings. If this is the case, the fan must be serviced as it is not likely doing it job and damage due to excessive temperatures may eventually be the result.
Note that the pitch of the whine - the frequency - may not even be audible to a technician assigned to address your complaint. The cutoff frequency for our hearing drops as we get older. Someone over 40 (men more so than women), you may not be able to hear the whine at all (at least you can look forward to silence in the future!). So, even sending the monitor back for repair may be hopeless if the technician cannot hear what you are complaining about and you are not there to insist they get a second opinion!