I've had a couple of iMacs now which exhibit a crackling noise from the lower left of the screen when the brightness is 5 bars or less. The lower the brightness the more likely it is to happen. The noise seems stimulated when the screen is rendering new content or especially in dark scenes. It seems to me low power usage is causing the components to crackle slightly. Does anyone else notice this problem? The noise is quite high pitched and more obvious in quiet environments. Interestingly, I installed windows via bootcamp for various reasons and in Windows this noise is not present at all suggesting it is a Mavericks thing. However, Mavericks measures 25 watts on lowest brightness, somehow windows manages nearly twice the power consumption however the screens are very similar in brightness at the lowest setting. I am therefore guessing Mavericks power management is playing some part. As I have had several of the new iMacs recently, some which don't have this issue, it must be a combination of panel + Mavericks causing it. I think windows high energy usage perhaps masks the problem as more power is being consumption. Having said that then it could be the PSU. //edit - looking at the iFixit photo of the teardown the noise is coming from the bottom left which is where the only fan exhaust is positioned. But the PSU is directly above. Odd. Maybe the noise is coming through the ports in the bottom of the casing.