I believe that the fan is hitting the GPU Casing for instance, when I'm on the computer, as it's warming up, the computer gets louder and louder and this doesn't happen in my other computer. The key difference between those computers is that my old one has the graphics card facing upwards. The newer computer has it facing downwards. This sound doesn't come from the GPU when placed inside my old computer. There is nothing in contact, no wires, nothing...
On a side note, I may have not been clear enough, so I'll do that, the fan is on the GPU for those of you who don't own this graphics card. It's not a fan that comes with the computer, it's used as an air intake to cool the 9800GT's GPU.