SRX240B2 fan behaviors

I have several srx240's. Two are "B2" . I have an srx240b also. The model with junos 11.4xxx is a quiet model. The fans only turn on at boot. The other B2 has 12.1xxx and the fans always run. High at boot, and normal at normal operation. The srx240b is junos 10.x and the fans always run.

Is there anyway to change this behavior?

I would like to make any given box run
silently.

Anyone have suggestions as I upgrade?