I have a dell poweredge server r720, I ran the following commands to lower fan noise in my home lab.
ssh to the idrac
racadm set system.thermalsettings.FanSpeedOffset 255 racadm set system.thermalsettings.ThirdPartyPCIFanResponse 0 racadm set system.thermalsettings.ThermalProfile 2
Example screen shot below
that’s it