Hello, i've had my computer for 2 years now. It's an ASUS CG8350 (http://www.asus.com/Desktop/Gaming/Essentio_CG8350/) I've replaced the video card, RAM and PSU for about a year ago. For like 2 weeks ago my computer started to make a high pitched noise when i play Fullscreen games like Counter Strike Source and CoD. The noise is not there when my computer is idle, it starts after being like 10-30 minutes in a game. I turn off my computer when i go to sleep and when i turn it on again when i wake up the noise is gone but returns when i play CSS (the same problem). When restarting my computer (pressing the restart button) the noise is still there when it turns on again. I think the sound comes from the motherboard or CPU or somewhere close to that area. The sound is very annoying... I've checked my computers temperatures and they are not higher than usual. (CPU 28-50 degrees celcius) (GPU 35-60 degrees celcius) (motherboard 20-30 degrees celcius)
its probably your heat sink or your graphics card, after about 30 minutes your cpu and gpu start to really heat up and the fans come on really heavy, i would say find a way to test them both. what heat sink are you using?
It's called coil whine. Coil whine happens as a result of interplay between two components with coils. It's usually the video card and the power supply, but the motherboard can also be one of the players.
The choices are using nail polish to silence the offending coils (you may be able to locate them better by using a cardboard tube such as may be found at the end of a roll of paper towels), or to RMA and hope the replacement doesn't do the same thing. The nail polish remedy does work, if you find the coils that are making noise, but I'm not enthusiastic about users having to spread goo all over their stuff just so the company can be cheap about not immobilizing the coils.
I think I've seen people say it fades over time but not quickly.