I found out the biggest noise pollutors are actually the two 7200 RPM harddrives

I made a similar discovery a while back. I was interested in quieting my PC down, and I tried an experiment where I simply disconnected every fan in the case for a moment (already had a "silencer" PSU) so that the only noise remaining was the hard drives. I decided that it was still too noisy, so I didn't bother with spending any more money.