A good way of eliminating resonance I once read about was to suspend the case fans from rubber bands. I don't know how you would do that the PSU fan though.
Vibration is greatly reduced when there is no direct contact with the metal parts. Even the Cpu can have a fan suspended over the CPU rather than fixed to the heatsink directly. It won't affect the cooling much if you get it close enough.
Read up on defferent mods and hacks that people have done to make their PCs silent. Some quite good advice out there especially about insulation and fan noise reduction.
