I have a Dell e521. The standard fan which is at the front of the computer runs pretty quiet most of the time. During heavy use like watching movies on wmp/vlc, streaming sites or some gaming the fan will increase speed and noise level which is to be expected.
However, there are some times when I notice the fan speed and noise increase when I am not using any programs at all. Most of the time this happens after I watch a movie tv show on wmp or vlc, and I leave it for a while and the screen shuts off into power saving mode and the fan will increase speed and noise.
I initially thought it was due to the programs being open but even after closing the media players, the fan sounds up again after the screen goes into power saving mode which is usually 20 minutes after not using the pc.
Checking task manager after doesn't show anything unusal or running at high ram/cpu numbers.
My pc has 2gb or ram which has always been sufficient for my usage, 250gb hdd currently with less than 10gb free. I'm now running windows 7 but I also noticed the same thing when I was running vista. The monitor is set to power saving mode after 15 or 20 mins but the pc is set to run, no sleep power saving mode is in effect.
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It's the front fan. My gpu doesn't have a fan and my PSU makes a slightly different noise. It's not so much the fan itself as it actually runs very well for a 6 year old pc fan, it's what causes it to increase in speed whenever the computer is in certain modes under a relatively low load, and usually when the screen goes into power saving mode.
So far I haven't noticed any pattern to what causes it, sometimes I'll leave the computer alone enough for the screen go into power saving mode and it stays quiet, other times the fan will start running really fast/loud until I move the mouse or tap on the keyboard to put the screen back out of power saving mode and the fan slows back down.
Sometimes, a fan with varying noise levels is the result of a bearing failure. It may even run "quietly" for awhile, then produce varying levels and types of noise (e.g. whirring, whining, chirping, grinding, etc) for awhile, then go back to being quiet for awhile.
The changes can be due to bearing variations due to the failing bearing itself, an external "bump" or vibration can cause the bearing to re-seat itself or unseat itself, or even minor power variations (whether due to power supply, other loads on the power supply, or fan speed control circuitry).
Such may also be caused by an unbalanced fan, although in my experience unbalanced small fans tend to produce a more consistent "grinding" or "buzzing" noise. An unbalanced fan will cause rapid bearing wear and early failure.
The Dell Dimension e521's "front" fan is actually the CPU fan. There's a large duct work that channels the heat cool air from toward the CPU toward from the front of the PC tower, where heat cool air comes out in through a "tunnel" opening (from left to right) behind the front panel. A picture worth a thousand words:
Turned out I was wrong about the direction of the air flow in my last post, it's actually an intake fan drawing cool air toward the CPU heat sink. See link below. The same link also mentioned the fan's spec as 120 x 38 mm. That's a little thicker than the usual 120 x 25mm fans, but you should still be able to find a replacement in stores. Again, good luck.
Usually, this problem arises after some months of usage of a new laptop. Mostly, it is due to dust accumulation on the CPU exhaust fan or due to lack of heat sink paste.
Use a blower ( not the vacuum) and then get rid of all the dust. At the same time, allow free air into your PC as it will help it to maintain its temperature by driving out the heat. Mostly use the PC beneath a fan or an AC vent.
Sometimes overloading the CPU with applications can also make the CPU processor work heavily and generate immense heat. This will automatically make the CPU exhaust fan work heavily and this will create lot of noise.
i use my fans for white noise to help me sleep. My fave fan is a Sunon 120x120x38 that pushes 98cfm. Sounds like a 747 but it sure can cool. i think I like johns post best. I've seen that config before with the duct going from the front to the CPU. fans are cheap. Replace that front fan and see if it fixes up your sound problem. If it doesn't it didn't cost too much. While you are at it, check out the label on the fan and Google for it's airflow CFM (cubic feet per minute) specs and dBA levels. that's the sound output in decibels. With newer blade configurations you can probably find a quieter and stronger fan to replace the stock Dell fan with. I use these guys for fans and accessories. Good prices and cheap shipping if you're gonna look on line. Called Silicone Valley Compucycle http://www.svc.com/
You can indeed place the steel lids from jam and sauce jars in your household recycling bin.
Please just make sure they are clean and dry.
You can put other steel items in aswell such as food tins,
biscuit tins and aerosol cans (just make sure they are empty and the lids are
offgeneric printer ink