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I recently installed a new CPU cooler, it works great but the CPU fan is quite noisy when I start the PC after it's been off for a while. To be clear, it's not a matter of fan speed, yes the overall noise is louder when speed is higher, but the noise it makes the first few minutes is there regardless of the speed. For the rest of the time it's very quiet at both low and high rpm, and the noise never come back unless I leave the PC off for hours.

I've tried touching the case of the fan both when it was making noise and when it was not, but I wasn't able to spot any difference in amount of vibrations.

The cooler was used, and very very cheap so it doesn't make sense for me to try to get a refund. Those two minutes of noise every day doesn't really bother me but I'm just curios on what could cause it, and if it could in any way harm the rest of the system.

This is the fan model: http://www.coolermaster.com/cooling/case-fan/blade-master-92/

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  • Looks like the computer is doing extra job in the period after startup.
    – iBug
    Feb 18 '18 at 15:38
  • @iBug That's what I initially thought, but task manager doesn't show any major activity (less than 10% cpu in use), temps are low, fan speed is about 900rpm (almost the minimum possible for this fan) and if that was the case rebooting should bring the noise but, but it doesn't.
    – flagg19
    Feb 18 '18 at 15:51
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    What about turning the computer off for 30 seconds and then powering back on? It sounds a lot like the bearing in the fan is dying and needs some time to warm up before it works smoothly again. If it was "very very cheap" then you have your reason right there.
    – Mokubai
    Feb 18 '18 at 16:22
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    Agree on the bearing issue. If you take the fan out and can put a little lube or WD-40 or something to get into the bearing area assuming it's accessible, then adding this extra lubricant may help with the initial noise until heated to make the balls spin more smoothly, etc. It is likely a temporary fix but for the immediate annoyance, it may suffice for your need until a more long term replacement occurs. Feb 18 '18 at 16:42
  • @Mokubai 30 seconds are not enough, 2 minutes is the bare minimum to bring it back even just for few seconds. Anyway I've searched for "bad fan bearing" sounds and it's totally like my noise. Thanks, if any of you wants to write a small answer, possibly adding how bad it is to ignore it, I'll accept it. Otherwise I'll do some more research and answer the question myself.
    – flagg19
    Feb 18 '18 at 17:05
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Probably some physics, with some component inaccurately manufactured, which gets stabilized once the fan and moving parts have run for a while and got heated up. Not much of course, but enough to create the noice initially and then get it to disappear.

That's my best bet, from some experience decades ago :-)

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    Probably something along those lines, It was working and as long as it didn't stop moving it would have been safe to keep it but... I got annoyed and replace it (just the fan)
    – flagg19
    Feb 22 '18 at 18:34
  • Yeah, that's usually the easiest solution. I assume there is no problem with the new one.
    – PatrikN
    Feb 22 '18 at 22:20
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This fan has a sleeve bearing. It is close to a normal ball bearing, but in this sleeve bearing you don't have balls but oil. (sometimes it has another ring between the stator and the rotor).

Anyway, if the fan is badly manufactured you have higher tolerances. (Sometimes you can cause this by bending the rotor).

AND what happens is all of the oil flows to the top, now the shaft holding the rotor isn't perfectly in the middle anymore. This then slowly disappears after the oil starts to distribute itself evenly.

The effect will return after some hours because the oil doesn't flow very fast (very viscous, like honey you can say, at least in these tight conditions).

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