Answer to a very old question -- but blade systems are dirt cheap on the secondary market now. We have a used HP C7000 Bladesystem chassis in our lab now, purchased for $200 fully populated with fans, power supplies, management modules, and a couple switches. It now has 3 blades, one storage array blade, two Cisco switch modules, and two 10Gb modules.
That package is far quieter than the screaming 1U Supermicro lab machines we had previously, and a lower pitch. As the lab is not in a data center, that change was very noticeable (and welcome).
When we previously ran two HP c7000 chassis full of blades in production in the timeframe of this question (2009), they were rather noisy of course, but that was in a data center. They seemed to comparable to the noise from a rack full of 2U servers and storage arrays, which use similar sized fans.