Hi Ch3m, have you tried mounting your pumps on foam, my res-pump combo vibrates a little so l mounted mine on foam, stops the vibrations coming through the case. If you can still hear the fans even though they are quite quiet turn some of them off, as your custom loop is not that dependent on case cooling, as long as you have some air flow your ok.
nah I havent mate, they are on some silicon mount things, which are on a plate. could possibly fit some foam in there but meh. Turning all fans off cept PSU one leaves the case with the same amount of noise, so it could also be the 13 hard drives lol.