Small inline fans make very little noise, and what they do make can usually be sorted by just mounting them with a small piece of rubber so it can't rattle.
The second question is really down to how you set up your grow. You can run it on the same timer as the lights, if it gets cold during lights out. Or you can have it on constantly for maximum odour control. Or just run it on a thermostat so it only runs when the room needs cooling, it depends on which are the most important factors in your grow.