Did you consider "rubber" padding that are availablel to put between your fan and the case to absorb vibration?
For everybody elses here, does it really work as "advertise"?
I installed silicone gaskets for all my fans and PSU on my latest build, and yes I think they make a difference. We're not talking about spending a lot of money for silence. I also installed padding kits in the two Armor case's I just bought and that has helped too. On my Armor Jr. (no window) I used the padding to cover both side panels and the complete bottom of the case. It made a big difference in sound and cooling, in my opinion. I did the same for the full size Armor case but didn't pad the side w/window. If I turn down the volume (speed) on my radiator fan (external) my full size Armor case is almost completely silent. I'm also using a heat pipe video card and haven't experienced any heat problems at all, CPU temp runs 28C idle to 34C load and motherboard temp runs 29C constant. I am using water cooling on the CPU.
Good luck,,,,,,,,,,,,,