Well after nearly shorting out my entire system (be very careful in there when you are doing any of these mod's btw - especially if the system is running as I did so I could test out some variations on the mounting), I have probably the ultimate method of making this fan quiet.
What you need is a sheet of that thin poly-ethylene packing material that they use to cover electronic gear with. It is whitish in colour and is 0.25 mm thick. If you cut a square piece 35 x 35 mm, then cut a 28 mm circle inside the square (just use a sharp knife it does not have to be exact) you will end up with what looks like a square shim with a hole in the centre.
Turn your machine off (Rondo and did the hard bit of testing all this so you guys get it easy
), remove the keyboard and heat spreader. As per Rondo's pic the fan is secured by two Philips head screws. Undo these and store them some place safe (you will not be needing them). Carefully place the polyethylene shim so that hole is clear and the corners of the square shim are covering the mounting posts of the fan. You will notice in Rondo's pic he has placed little pieces of foam against the posts. With the polyethelene sheet you will not need to do this because when you replace the fan it will force the sheet down between the post and the outer frame of the fan, thus mechanically isolating it from the motherboard.
Carefully hold one corner of the shim in place with a pair of tweezers and push the fan back into place. You may need to adjust the shim slightly so both corners are packed correctly. You should notice that the fan is securely held in place by the polyethelene shim against its mounting posts. DO NOT replace the mounting screws. The heat spreader will hold the fan in place.
The whole idea is to mechanically isolate the fan from the motherboard. If you listen to Rondo's wav files using Windows media player and set your view to bars (effectively a fourier transform into the frequency domain) you can see the fundamental frequency that the fan resonates at. It is this that we want to dampen by use of "accoustic shock absorbers". The shim, or my original pieces of heat shrink tubing or Rondo's foam all act to decouple the fan's resonance from the motherboard.
Since making the mod to the fan my system has quitened down considerably. I can now even hear the hissing air in the pipes during the intro of the ATI Pipe Dream graphics demo program.