i think it was gandalf perhaps who did it i cant remember enough to find it though.
i would recommend going to your chemist and getting some earplugs, nearly as cheap and much much less fiddly. or perhaps the whole hog and getting some of the 'proper' ear mounts.

mynci

Leo used foam to mount fans in his system -- Quiet MP Dual-CPU Workstation

Ear plugs were discussed a bit in this thread --- A suggestion I heard...

If you are considering using that carpet padding to mount/isolate your HDD, you may want to find out the temperature rating for the adhesive. You don't want that stuff melting or drying up and making your HDD crash to the floor of your case or HDD rack.

Beyond the adhesive issue, I really can't tell from the pictures, but is this material either elastic enough or thick enough to isolate HDD vibration?