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After switching off the monitor, there's a single crack after a while. I wonder where exactly it comes from.

I know that this is normal and not an indicator of being defect. This sound is also not related to a specific type of monitor. I've heard this sound from my CRT as well as from my TFT.

I guess it possibly has to do with cooling down. I found a lot of statements that second this thought but there's no reliable source confirming this theory though.

However, an explanation that only says that it has to do with the cooling process is not sufficient at all. I'm interested in what exactly makes this sound? Is it, for example, a capacitor which has fully unloaded (if this is the proper term). I really haven't the slightest inkling what exactly can make this crack noise.

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up vote 3 down vote accepted

Yes, it's the cooling down. This happens mostly with CRT monitors (I've own a lot) and could still happen with LCD monitors (rarely, mostly occurs in cold temperature). Electronic components wouldn't be the source at all.

Capacitors don't make a noise when it discharges gradually which is assumed. If it does then the world would be a bad place to live (too much dB).

Things I can say to be NOT the source of sound are:

  • electrical components: The only electrical components that makes a noise are speakers and relays. Both are eliminated as a source since a speaker probably don't exist in a typical CRT and, though a relay may, a relay only makes a single tick sound - a quiet one.

  • static: it can't be static, a crack and static sound barely have similarities.

To be concise, the sound is simply the case. That's why this seems to happen more often in colder weather is because when the monitor is turned on it heats up (especially CRTs) expanding the case a bit, and during cool down, the manufactured plastic will start to change shape in edges causing the sound, and in colder environments this will tend to be more pronounced because the collapse in a greater magnitude is like to occur more.

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+1 for perhaps "I kinda didn't know that" :-) –  Waffle's Crazy Peanut Dec 17 '12 at 16:48
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