HP M6720 Fan Mod

Decided to replace two 15-bay rosewill chasis (bottom two) with a head units and disk shelves. Ended up with a Dell R720 8-bay LFF and a HP M6720.

The Dell is no louder than the Rosewill, but the HP is so loud that can be heard with the room door closed. I am thinking limiting the fan speed by adding a physical controller to all its fans.

It turns out that all the fans are in the power supply. Here is what it looks like inside the power supply.


Model Number:

Close-ups on the fan connector: (I assumes it is two connectors for two motors integrated into a single fan housing? the other wire is the status LED on the back of the metal case)

What is the best path forward to reduce the fan speed? It is a 4-pin connector so I assume it is reporting the RPMs back to the controller and receiving PWM signal from the controller to control the RPM. If I simply reduce the fan speed, the controller will try to compensate, and it just end up running at max. Any suggestions?