Dell released version 4.40 for the chassis firmware.
Incorporated in that release is a racadm command to change the minimum level for the fan speed.
e.g.
After applying this firmware version to the chassis (4.40 or above), the minimum fan speed can be adjusted, via a putty session, by the following (example changes fans to 50% max):
racadm config -g cfgThermal -o cfgThermalMFSPercent 50
To see what the fans are then doing type: racadm getsensorinfo
I know it's not really a fix, but it gets past the problem of fans ramping up to jet engine noise levels so that working near them becomes a nightmare. What this does (for us) is keep the temperature down to <60degrees C so that the fans do not ramp up to >9000rpm