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Whirring sound coming from PC

April 16, 2009 at 00:12:33
Specs: Win XP Home, P4 1.6 GHz/512MB

My computer started making a whirring sound last week that I'm sure is the PSU fan. I turned the computer off and didn't turn it on until yesterday so I could back up files that I had recently downloaded. The computer sounded fine so I installed two temperature monitoring programs to keep an eye on the temp. After about 30 min, the noise started again. According to the two temp programs, everything seems to be fine. There's no change in the fan speeds when or after the noise starts. However, when I look at the PSU fan, it sort of looks like it's spinning slightly slower or it could just be spinning wobbly. According to the two temp. programs, my computer only has two fans: CPU and PSU, which is where all my questions come in.

I see two fans on the back of the computer case. One is obviously the PSU fan and it seems to being blowing air out (judging by the cat hair stuck to the case) and looks rather dusty. I'm not sure what the other fan is for/is called but that seems to be taking air in (judging by the cat hair stuck to the case) and is cleaner than the PSU fan. Is it normal for the PSU fan to blow air out and the other fan to take air in? I always thought it was the opposite. What is that other fan on the back of the case? Is it an exhaust fan or CPU fan? Shouldn't I have another fan inside the computer?


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#1
April 16, 2009 at 01:05:59

Generally you want air coming in the front and going out the back. So fans in the back of the case should be blowing air out and any fan in the front should be pulling air in.

If you can't tell which way a fan is blowing, take a look at the center hub. In all the ones I've comes across there is a sticker over that center hub on the 'air out' side. So if you look through the grill and see a sticker, that fan is blowing out.

Some cases have fans in the side. I'm not sure if there's a set rule for them. I think you'd want to balance the air flow so that if (for example) you had 2 fans in the back, one for the PSU and one for the case, then maybe a side fan would be pulling air in.

If you're unsure about which fan is making the noise just temporarily disconnect it. If the noise stops then that one is the problem. For ones you can't get to, like the PSU fan, stick something like a screwdriver blade in to keep it from spinning. Don't stick it in when the fan is spinning, else you may break the fan blades. Put it in and then turn on the PC. Also don't push it in too far or you may contact the PSU electronics.

Sometimes you can lubricate the center hub of a noisy fan and fix it for awhile. However, I always replace the fan, but then I've got several dozen good fans from old systems I've scrapped that I can use.

Oh, and about your monitoring programs that only shows 2 fans: Only fans powered from the motherboard can be monitored, plus there's usually one or two fan headers on the motherboard that aren't monitored. And often case fans are powered directly from the PSU with one of the extra drive power connectors. Those can't be monitored either.


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