The BMC/iDRAC in is programmed to set fan speed min/max and adjust values based on factors like ambient temperature and system configuration. Depending on configuration the system may run the fans at higher RPMs regardless of any detected temperature. But...

If you use server at office, the noise become very anoying. If you set Maximum Performance in BIOS (Power Management),  there is no way to adjust fan speed because when server start, IDrac set Fan Speed Offset to Max...

Many people advise changing the fans or changing the BIOS, but I found that very risky...  The way i used is changing the thermal FanSpeed Offset value in IDrac.

Fan speed and temp before adjusting...

SSH - iDrac...

 

Get SpeedOffset value:

racadm get system.thermalsettings.FanSpeedOffset

Set SpeedOffset value:

racadm set system.thermalsettings.FanSpeedOffset X

The X values are:

• 0 - Low Fan Speed
• 1 - High Fan Speed
• 2 - Medium Fan Speed
• 3 - Max Fan Speed
• 255 - None

Fan speed and temp after adjusting...

There is also benefit with power consumption. Before adjusting, server used about 250W and now is constantly on 120W...

I used this on PowerEdge R620 but this adjustment can also be used on other Dell servers with noisy fans...