I'm having fan speeds and noise level issues from my most recent batch of HP ProLiant DL380 G7 servers. Most of the systems are nearly silent with low fan speeds (as reported by hplog -f ). The majority of systems causing issues are running an operating system that cannot accommodate the HP Insight Management agents or drivers (NexentaStor 3.1).
Fans are usually the noisiest items found in a computer, and often run unnecessarily fast - a 1.5GHz Athlon may well need the fan to be turning at 4,500 rpm, but a lesser machine with a good quality heatsink probably doesn't. One situation where a slower fan is definitely beneficial is when a CPU fan in an older machine needs replacing.