The case is made of pretty thin steel and light, hard plastics. Hot-swap hard drive mounting has barely any damping at all, so most of the vibrations, seeks etc. transfer to the case at full power.
That meant I had to do a few modifications. I bought 4mm thick self-adhesive Nikesound bitumen mats (they add mass), 40x50cm each. Two of those to the side doors and part of the third to front and back and around the hd case added some mass and reduced vibrations.
I also added some sound dampening foam to front and back of the case. I had to turn the PSU around to take air from inside the case because of unbearable coil whine escaping from back.
7200rpm Samsung got elastic suspension.
With these mods the case is reasonably quiet when the 18cm fans are @ 600rpm. I removed the 12cm fan from top.
Top plastic cable cover still rattles, so I need to dampen it too. Meanwhile I put a cast iron mini anvil on top of the case to stop that rattling.
I really hope Silverstone comes up with better hard drive damping systems in future... Antec did that right back in 2005 already, SS should really get on with the times. If they can't figure out it by themselves just copy the transparent silicone grommets from Antec and be done with it..