There it is, i changed my hosting. Well I changed my multi purpose computer. I switched off my good old server which once was my primary workstation. A watercooled Opteron 165 dual core in a giant Twelve Hundred case by Antec. I now use a mini-itx pc based on an Intel Atom D510. Perfomances probably decreased but it now fits in a Fractal Design Array R2 ! Elecricity consumption and noise are more manageable now.
This new machine is fanless (more or less) without watercooling (no more gloo-gloo). The silence has come ! I moved HDD to this case (and added one). This box mainly serves as a router and NAS (with 6 HDD maximum). It was quite easy. Only had to tell grub to boot from the right disk (3 tries before choosing the good one) et and voilà ! Gentoo was up and running.
PS 2017 : I still use this machine 7 years later. This website is served by this small Atom. It no longer is a router as I baught a dedicated appliance.