Getting Rid of the Power Supply Fan
With the side and rear off, you can gently remove the bottom. There are three plastic latches and two posts that fit through female fittings holding it on. Gently depress the latches and gently tug the posts out of the fittings to remove the bottom. In Figure 2 below, you can see the post-and-latch arrangement. The latches are visible closest to you, as are the posts; the female fittings are resting close to the work surface.
Figure 2: Bottom Cover Posts and Latches
Next, unfasten the power connector from the power supply to the motherboard. Unfasten all the screws on the motherboard, and gently disconnect it from the RAID daughterboard. This gives you access to a screw that holds the power supply in place, at the front of the unit, facing the motherboard. There are two screws at the rear of the unit (or was it three?) which hold the power supply in at the back. Unscrew them, and gently tease out the supply.
Figure 3: Motherboard exposed
Figure 4: Removing the motherboard provides access to this screw
There are multiple screws holding the power supply cover on. One is under a label voiding the warranty, one is under the product identifier label. You have now irretrievably voided your warranty. The others are all visible, but it took me a little while to find the one under product label. Gently pry open the power supply. Cut the power leads to the fan as close to it as you can, and tease them backwards. They can be threaded out with the power yoke and redirected up through the grille to power an outboard fan.
As long as you're there, you might as well pull out the fan unit itself. Definitely pull the clear plastic shielding out of the power supply. It's on the inside, over the ventilation grill that sits above the heatsink. With the unit mounted heatsink-up, that will be the heat exhaust surface. Note that there is no room for a fan inside the chassis above the power supply.