Have times gegoogelt Pros Sonata and a 550-EC found housing, but this is not so easy to get.
Why "not easy to get"? http://www.amazon.de/gp/offer-listing/B000Y9VOBQ/ref=dp_olp_2
Only with the housing alone will not get far. The best as many components as possible to "Silent" convert: http://www.silenthardware.de/ http://www.pcsilent.de/
passively cooled graphics card, Processor NEN Heatpipe Tower ", synonymous fanless power supply or fan, then a few quiet 12cm fan into the housing construction to provide a cooling airflow to maintain.
Hard rubber frame at all, all the drives that you do not need to go. (ie s.besten only one, maximum of 2 hard disks)
And then next, and so forth - google search: Silent PC, silencing - are many pages with tips.