My system starts off quiet but then after 5 mins or so everything starts heating up and the fans start speeding up and before I know it, I can barely hear myself think over the noise from the fans coupled with the vibrations of the case. I can't say I know what brand of fan I have in my machine but what I can say is this is a custom built machine from a private business, that is it was not built by a mega-corporation or chain store.
The whole reason I want to make things quieter is I just bought a new set of 5.1 speakers and because of where the computer is located (which cannot change due to desk configuration) the noise is directly below the center/left and right channels.
Any solution aside from the 'attach a refrigeration system' will be appreciated. I am using a Intel P4 3.06 GHz with a ATI Radeon 9700. If there is anything else I can tell you which will help you answer please let me know.
(1) If your machine was assembled with cheap fans, then brand name high yield fans may still be notably quieter than what you have now (although they still may be somewhat loud)
(2) Many quiet fans are available in the low 20 db range. For example, Vantec Stealth fans run at 20 DB, which is barely audible (I have 6 running in my case and could barely hear my PC -- my hard drives are louder than my case fans).
Very quiet (low yield) case fans come with a price, you get silence at the cost of air flow. quiet fans may not make alot of noise, but they won't cool off your case as efficiently as high yield fans.
The first thing you should do is measure your CPU temperature to see if your current fans are overkill. If your mobo has onboard sensors, then you just need software, otherwise you may have to go with some third-party temperature sensors.
If you choose to install low yield fans, monitor the temperature closely to ensure they are strong enough to keep the temperature within tolerable limits.