Yes, it's a very quiet noise, you can only hear it in a totally silent environment and you need to have a good hearing, older people usually can't hear it as it is a very high frequency.
Yes, for the most part they are talking about another problem, but there is at least one reference to a high pitched noise related to the brightness of the display there.
To clarify, the noise/buzz varies in volume depending on the backlight setting. It's loudest in the middle settings but yes you can clearly hear it stop and start by switching between off and the 1st square of brightness.
The noise is actually composed of many frequencies but the strongest is in approximately the same range as the fan buzz. In my case the right fan masked the sound enough that I didn't hear it from the screen at first. Still, on all 17's I have seen, the noise is at least as loud as the fan and is usually the loudest thing on the machine.
I disagree about needing a "silent" room to hear it; sure silent is relative, but once you notice it's pretty easy to pick out in what I consider a normal working environment. Again, with 16 different backlight settings there are 16 possible volumes for the noise, but it's always there and really should not be at all.
I wanted to use my 17" MBP partly for audio work and this is pretty annoying for me, but I would guess at least 50% of people will never notice. Here's hoping someone at Apple does... eventually. Since the 15" was not an option due to audio problems of their own, I've completely jumped ship and gone to a black Macbook paired with a desktop LCD. Loving it, and both are dead silent.
AFAIK LEDs are driven by a constant low voltage, e.g. 5V (which needs to be produced by some inverter as well, but which usually is not part of the display). The brightness is controlled through PWM (Pulse Width Modulation), which basically turns the LEDs on and off in a certain frequency (fast enough so the eye won't notice) to achieve the intended brightness. IIRC the brightness of a CCFL tube is controlled by the voltage applied to it, also the voltage is much higher, e.g. 30000V, thus an inverter is needed to control the brightness in this case.
Personally I believe there is a problem in the circuitry which generates control signals for the backlight, something like a capacitor too close to another element or something else like that (I'm no electrical engineer
) )Personally I believe there is a problem in the circuitry which generates control signals for the backlight, something like a capacitor too close to another element or something else like that (I'm no electrical engineer
Since this circuitry seems to be software controlled you probably can play around with certain parameters to try to eliminate the noise but I would not put much hope in it, since this seems to be more of a general fault (I'd love to get proven wrong though
