This setup is… well, puzzling. He seems to be going for absolute maximum performance and noise be damned. The extra Giga fan will more-or-less work where it resides right in front of the original main fan, but the turbulence in that section gets loud indeed. The PCI-slot exhaust fan he has in the "top" slot adds even more noise, plus it works against the main fan by sucking already-hot air up from the CPU area, across the VNF100 and the other PCI cards instead of it going right out of the back exhaust opening. I know this because I tried that exact fan in that position and it actually raised the internal temps.
Maybe he has the MDD in a separate room.