Question Baffling Fan Sound Issue

Jan 15, 2023
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I've got a custom built air cooled PC. It's been about 6 years without any issues. I shut down the PC one night, and the next morning when I switched it back on, one of the fans was making a loud horrible noise, like something was being hit by one of the fans. It seemed to me like the sound was coming from the back. I shut it off and opened it up to see what the issue was, but couldn't see anything out of place. It had been some months since I last cleaned it, so I got rid of most of the dust and figured I'd turn it back on to see if I could better pinpoint the issue. No weird fan sound. I figured that by moving the PC or cleaning it up, I must have somehow dislodged something. I continued on with regular use. About 13 days later I started it up again and had the same issue. Again, I tried to locate the origin of the sound. This time I was sure it was coming from the front. Either a hard drive or one of the front case fans. Out of pure curiosity, I did not manipulate the PC in any way. I simply turned the PC off and switched it back on. This too, fixed the issue. It's been maybe a week since then, and it just happened again. I tried the restart method, and again it worked. The frequency of the noise seems to fit with the speed of the fans, and when shut off, the noise gradually reduces in frequency until it gets slow enough, and abruptly stops, much like a fan with extra friction would do. I have just a couple ideas for troubleshooting this. First would be to watch the fans while the pc shut off when this sound is happening so that I can tell which of the three front case fans is doing this. (Assuming it is one of them). The other would just be taking the computer apart and fully cleaning it all out in case I've been missing something.

tl;dr: I have a case fan that makes a grating noise roughly 10% of the times that I start my PC. This sound goes away as soon as I shut the PC down, and only ever comes back again on a random startup.

Has anybody else experienced something like this?
 
Jan 15, 2023
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0
10
This sounds like a wire/cable may be making contact with a fan. This is a fairly common occurrence and can usually be isolated by visual inspection/stopping fans one at a time (be careful doing this).
It's not a wire. There aren't any loose wires in the vicinity, and none of them are even remotely close to being able to contact the fans.
 

Karadjgne

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Sounds like worn bearings in a fan. If you figure a fan has very specific weight and blade pressure requirements to maintain perfect balance at higher rpms, it'll wear in a specific way. Then you clean the fan, or even stop it, and that can shift where the bearing was sitting. Start it up again and it's sitting in a slightly new position, out of its comfortable groove. Then it gets noisy.

Sometimes shutdown can let the bearing go back to its wear spot, sometimes it's cranking the rpm higher than normal, there's no real rhyme or reason to it why it works 90% of the time and is noisy just 10%.

If the bearings are worn, there's only 1 fix. Replace the fan.
 
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Jan 15, 2023
6
0
10
Sounds like worn bearings in a fan. If you figure a fan has very specific weight and blade pressure requirements to maintain perfect balance at higher rpms, it'll wear in a specific way. Then you clean the fan, or even stop it, and that can shift where the bearing was sitting. Start it up again and it's sitting in a slightly new position, out of its comfortable groove. Then it gets noisy.

Sometimes shutdown can let the bearing go back to its wear spot, sometimes it's cranking the rpm higher than normal, there's no real rhyme or reason to it why it works 90% of the time and is noisy just 10%.

If the bearings are worn, there's only 1 fix. Replace the fan.
I've been leaning in this direction. That makes a lot of sense. I think you're right. If the fan shifts a little every time that it shuts off, there could very easily just be a certain position that it has a chance of shifting into to cause the sound on the next startup. Then after another shutdown it shifts again back out of that position. Thanks for the advice. It's just one of three front case fans, and when it works it works, so I don't see the need to replace it yet. I'll probably keep running it as is unless it starts doing it more frequently or when the PC is already running. Now that I think about it, I guess I've been lucky so far. Never once experienced a broken/worn to the point of failure fan in any of my computers in the past.

If I change out the fan and it solves the issue, or if I find out that something else was the problem, I'll come back and update this thread.