Forum Moderators: open
you cant find anything about fan noise ..becasue they dont expect it to be suffering from fan noise ..
and even an old machine running a large fan doesnt get past the mid 40's in db ..
90db is a Harley on tickover at 3 feet or less ..
The biggest factor in fan noise is the diameter of the fan. Larger diameter = lower noise. In a 5U server, the fans should be big. 1Us are notorious because of their use of "squirrel cage" fans, which are noisier still.
That said, server makers really don't care how noisy their fans are.
If you want to break the warranty, you might substitute a fan with a temperature sensor, if the PS fan runs at full-blast all the time.
Do make sure you get one that is capable of high RPM. There really is little variation in noise at a given RPM between competing brands of "low noise" fans. The noise is almost entirely determined by the RPM. A lower-noise fan, in most cases, simply runs at a lower RPM! What you want is to control the speed with temperature, but make sure the fan has high RPM for when you need it.
I like Thermaltake's Smart Case Fan II. It comes in a kit with a temperature sensor and variable resistor, so you have your choice. Full speed is 4800RPM (for the 8cm model) which is quite a blast (AND quite noisy!).