Thank you all for your comments.
You were right. The vibrations are caused by the HDDs (and DVD). I have to admit - very disappointing construction, Antec.
I attached two pictures of my current configuration. As you can see, there is a slight room between the HDD and the case. I'm wondering what is the best course of action in my case (pun unintended).
Should I try and use rubber grommets (will they fit in?). If so, should I go for Nexus (like in http://www.nexustek.nl/NXS-nexus-mtk-60 ... ingkit.htm
) or is any generic rubber that I get in a hardware store is good enough?
I might opt for a dedicated solution, like http://www.nexustek.nl/NXS-doubletwin_h ... _white.htm
, but I'm not sure it can fit in my case. Plus I'll still need a solution for the DVD drive. BTW, is the item I listed the best solution or are there are comparable (or better) devices?