Yeah I think your right it is the center. The center one though is closed. I saw some videos of people applying oil to their fans where the back is closed off like mine. They used a little drill bit and turned it by hand. Then, sucked out the plastic shavings and applied oil. I am going to put the sides of the case on and see how loud it is. If it is really annoying I will try the above, or applying oil from the side like in your pic.
Also, I wonder if the above wattage/heat is correct for the i7 3770k? I tried using the PSU calculator to get a rough idea of the wattage of and i7 3770k overclocked to 5ghz with a max vcore of 1.35 and it said almost 200w though. Seams like the 100w for OC for the i7 3770k that Knufire posted is a little low but I'm not 100% sure.