I see you mentioned the new Seasonic X-560 / X660
I only considered PSU reviewed by SPCR
do you know have if it features the great noise performance of the older review here?http://www.silentpcreview.com/Seasonic_X650
Well its the same line, they should behave similar, persnally i own a X 660 and i dont have any issues, passive at idle, very quiet at load, i think all the series would be a good pick just a matter of chosing the right wattage for you, that said, even the SPCR reviewed X400
, some people experience buzzing sound, check X-400 buzz noise
, or even the one you are considering, Seasonic X-650 - buzzing
, still i went x400 and x660, both working perfect for me, i think its more the combination of hardware or bad luck, regardless seems a very low amount on the user reviews experiencing, so i think its low the chance, but its best to know it can happen before you commit.