Well, I didn't really feel like making another account on some tech forums so I figured I'd start here.

My problem with my fan(s) is that whenever it goes into sleep mode then comes out (even if it was only asleep for a few seconds) at least one of the fans goes on full blast and makes this horribly loud noise. No matter how long I wait, the fan doesn't slow down; it just stays really really really loud.
It doesn't fix after restarting the computer, instead I have to turn the computer all the way off and turn it back on, if I get lucky the sound goes away.
Sometimes I have to keep turning it off and on several times before it returns to normal, and waiting a few minutes doesn't help at all.
If I use my computer and it never even enters sleep mode and I shut it down, then upon turning it back on even before the OS loads, the fan still goes as loud as it possibly can.

x.x I don't get why it does this.

If it's making a horrible sound like you described, I would open it up, clean the fan and check if anything is broken, also I would check the temperature.

might be some plastic stuff in your fan, wires. w/e, if its a case fan just take it out

If you computer is a desktop, take it apart and clean the inside of it out. Its most likely that you have a lot of dust and a lot of other crap inside. If it is a laptop, make sure you know what you're doing and do the same thing. Also, make sure you have one of those cans of sprayable air. It help out tremendously.

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You could always try using SpeedFan to control the speed of your defective fan until you can buy a one.

You could also try changing the various power management and/or fan speed settings in your BIOS if your motherboard allows you to.

B.T.W. what fan(s) is it? CPU, Case, Power Supply? Use a straw and listen if you can't tell.

Now this is a worst case scenario, but it happens. It could just be your computer is dieing. Similar thing happened to my first computer. It sounded like a small jet engine in it's last months before it started smoking one hot summer afternoon. It smelled of melted plastic. It wasn't so catastrophic. Sure the motherboard and CPU were cooked, but somehow the RAM and my hard drives were fine. In any case if you aren't already doing it, backup your stuff.

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if you hear that something is wrong with your fans, it's quite stupid to let it run like that for months... The most likely reason that why your motherboard and CPU were cooked is that the CPUs fan cave out.

and now back to topic: Like the others said you should open your PC and clean it up from dust and test if it still makes that sound after it. If it still does it, there might be a wire somewhere hitting on the fan or the fans bearings are giving up. In this case you need to buy new fans, which arent expensive, but if it's the CPUs fan then you need to buy thermal compound too.

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Errrr.... Some people seem to be misunderstanding something. When I turn it off and back on, sometimes the fan doesn't instantly go crazy and it NEVER goes crazy for the days I leave the computer on - UNLESS I turn the computer back off or put it to sleep. So far it has literally had a 100% chance of going crazy upon being put to sleep, and maybe 3/4times when I turn it all the way off overnight. That is why it would be unreasonable to think it's dust or a loose wire or something (by the way I've already dusted it out several times / checked for loose wires)

Which fan are we talking about? Case fan? Video Card fan? or Heatsink fan?

Have you tried turning it on with the side panel out and observing. It might be something else that's making the sound and you just assumed it's the fan, It might be the harddrive, I had one that did the same thing.

Its probably defective. Do you have an additional graphics card installed? If you do, then they need a dedicated high powered cooling fan. I suggest you call up the manufacturers and ask them to repair it, or simply replace the fan with a new one. If your fan isn't working properly, you should avoid using your computer too much. Don't ignore the problem as it can lead to a meltdown.

I am willing to bet on it being the CPU fan. When waking from sleep mode the fan controller, (marked by the four-pin connector on the mobo), is not being properly reinitialized. First steps would be to look into a possible mobo firmware update and see if you are current. Next I'd look at all applications that are running in the background during the sleep cycle. Any one malfunctioning application can cause odd performance if it leads to a CPU spike and redline.

Disable a few applications. Or even try all this in safe mode. See if a cold boot into normal with a forced sleep will cause the issue. See if a cold boot into safe mode with a forced sleep will cause the issue. Start looking at possible software quagmires.

~~Dos

(PC Hardware tech, not so much on the software front, but an educated guess never hurts.)

Is you system a stock prebuilt computer with random manufacturer OEM software installed on it? Sometimes they can have their own software that handles fan speeds and adjusts them accordingly to computer temperatures. That might just be the thing.

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You think I didn't try everything to fix it before it got to that point. What I was trying to get across was that by that point there was nothing to be done except wait for it to die. I will grant you this boon. At that point I was fairly new to computers and I shouldn't have let it get to that point, but I did. And roasted silicon was the result.

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Sarcasm just doesn't work over the internet.