I presume the "Jet Engine" noise is due to having so many case fans and not because of noisy HDD's.Therefore adding SilentDrives wouldn't really serve any purpose.IMHO

A better option would be to lag the case with sound proofing material.There are many sound proofing products around and most overclocking stores will stock them.

Just as an example,here's a review by Frosty Tech of a product called Melamine Foam.