[Le Flaneur]

I'm talking about the late 2005 models with CFL-backlit matte LCD panels, not the new LED 24" units. In a very quiet room, if I put my ear to the top horizontal surface, I can hear a hum (which is also sometimes audible when I'm working about 18" away.

Can anyone else hear the hum from their ACD? I'd also be interesting in hearing from those who hear absolutely no hum.

[ghporter]

CFL illumination requires high-frequency devices to produce the voltages needed to operate the cold cathode lamps. With age, the components that produce the high frequencies can begin to physically vibrate, producing a hum or buzz.

It's not terribly uncommon to hear such displays as they get older.

[Le Flaneur]

Originally Posted by ghporter 

CFL illumination requires high-frequency devices to produce the voltages needed to operate the cold cathode lamps. With age, the components that produce the high frequencies can begin to physically vibrate, producing a hum or buzz.

It's not terribly uncommon to hear such displays as they get older.

Thanks. Apple tech support seems willing to try to resolve the problem (since I have AppleCare), and they've replaced the LCD panel and the logic board already, but I can still hear a bit of a hum.

Is there anything else replaceable that could cause the hum? What about the CFL backlight tubes themselves?

[Veltliner]

My 24" white iMac developed a terrible hum after about six months. If you turned it to full blast brightness it was almost gone. The lower the brightness setting, the louder the hum.

It was a technical part that upped the voltage. As it was part of the screen, the whole screen had to be exchanged (warranty).

[seanc]

Most likely the inverter. 23" ACD has an external PSU doesn't it?