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So, this question has been bugging me a lot, I used to have a few lovely little toys (well, not so much toys as a pentium pro and a really old Intel 80386DX microprocessor) What I noticed is that when the CPU's are under load they generate a most delicious noise which reminded me of when I used those computers for actual things (the 80386 had DOS 6.2 at one time and I ran a small unix server on it a few years later, the pentium ran windows 95 and then later windows 98+ and even later I somehow barely got xp running on it), I almost dare say it's nostalgia.

Anyway, that noise made me curious, what causes it? My first hypothesis for this rumbling/humming sound is the fan, so I tried removing every last fan, the noise didn't stop, it was actually easier to hear when the whirring of the fans wasn't there, I then spent hours testing each piece of hardware and came to the conclusion that the CPU itself was making the noise and then decided that I was happy with my conclusion for then, I recently remembered it and I got curious as to what generates it.

I don't own those machines anymore (alas I had to get rid of them due to moving) but I have observed that newer CPU's make the same noise, just a lot fainter and more subtle, so I do think it has something to do with the underlying architecture.

Anyway, before my rambling carries off too far... What causes the noise and is there any correct terminology for it? These questions are derived from a few hours on google and getting nothing but people asking silly questions such as "Why is my hdd ticking?" or "Why is my CPU producing a high pitch noise?" (the latter is closer but not what I am looking for as the noise is low pitch and quite distinct, if you've heard it you should know what I'm talking about)

I want to know this for a couple of reasons, curiosity is one but I also want to utilize this sound effect in a project of mine.

Now, some of you may point out that CPU's have no movable parts and are thus incapable of generating noise, then what could possible causes be? I tried removing everything redundant from those machines and the sound prevailed, the only things I didn't remove or replace was the mobo's and the cpu's themselves (because finding such old hardware proved harder than expected. oh and this part is what really sparked my curiosity as to what was generating the sound as the fans were silent when just powered on, and the machine kept making noise without them (I ran them at short 1 minute intervals))

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Get a Mic, stuff it down there, where your ear cannot fit easily. I heard a low dampened clamping sound too a few very quiet times. You have magnatism at the coils and transformers. an Odd one is many of the metals expand and contract at differing temperatures. I have always believed in a molecular movement between the sync and the cpu die due to different expansion rates. Copper around ceramic? Transformer lamination? even possilbe that the rolled plates in caps make a sound on high energy. It would be interesting to "label" the specific noise. –  Psycogeek Sep 28 '13 at 10:25

3 Answers 3

Are you talking about Coil Whine? Here's a differently pitched example and strobed example.

This can be cause by bad power supply, high load, bad grounding...

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Most definitely not, that sound is way too high pitch. –  CubeGod Sep 30 '13 at 2:33

Sorry, but it could not have been the CPU. Maybe you were picking up some sound from the speaker/on-board buzzer of the device had one (possibly line noise ?).

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As I pointed out it's probably not the CPU but what made it baffles me. Neither of the mobos had on board speakers or anything of the such which is what puzzles me, a barebones setup with mobo cpu and psu, everything else (except a heatsink, left in place for obvious reasons) was stripped. It wasn't a coil-whine, it was too low pitch and varied for that (well, at least in my experiences with whiny coils) The PSU itself was tested in other machines and did not seem to be the culprit, neither did any of the other ones I tried. Could it be some component of the mobo? –  CubeGod Sep 28 '13 at 6:34

You might have already done this, but you didn't mention eliminating optical or hard drives as possible cause. They often make low pitched noises. The CPU itself shouldn't be making any noise, but there are other things on the motherboard can. David mentioned the possibility of a buzzer but capacitors can also make noise, especially towards the end of their life.

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Yeah, I eliminated those too, my barebones setup was when investigating psu, mobo and cpu (well... that and a heatsink left in place for obvious reasons) Faulty capacitors don't sound at all like what those computers did... I really wish I had them still, I would record a sample (why didn't I think of that before I threw them out anyway?) –  CubeGod Sep 28 '13 at 6:39

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