I just bought a Seasonic Platinum 400 power supply. I installed it in my PC which otherwise has no moving parts. The power supply is not silent at all, and clearly some of the electrical components are vibrating. Unlike other people here, I can hear mine from all the way across a room (25 feet away), even while watching TV. The sound is not constant. There is a baseline buzz, followed every few seconds by a much louder higher pitched clicking/scratching type of sound, almost similar to a spinning hard drive. When my PC boots it always stalls and says 'CPU Fan Error! Press F1 to resume.' This is because I have no fan. At that moment (low load?) the supply makes almost no noise (I have to put my head right next to it to hear anything). But as soon as Windows starts up and higher loads are drawn, it makes a lot of noise. I am tempted to return it but I'm a busy person and it already took me months just to find time to buy it and install it. Anyhow be warned. To be fair it is still a lot quieter than my old supply that had a fan.
On the other hand my Zalman FX-100 fanless CPU heat sink is a marvel of a product and one of the best purchases I ever made.
Return it. Nothing quite sucks like disassembling a PC and waiting on an RMA but you'll never be happy if you don't.
I have been VERY happy with my Kingwin Lazer Platinum:http://www.silentpcreview.com/Kingwin_L ... um_LZP-550
I know they are tough to find but it's been great to use. I haven't noticed the fan kick on yet, even during gaming. I don't have the most powerful rig (Z97 board, stock-clocked Haswell refresh i5, Geforce 770, a few other goodies). No coil whine, and while my system isn't DEAD quiet, I can't hear the fan when I manually switch it on from two feet or so. It's a great unit. Maybe a bit pricey for 550 watts, but it's Platinum rated and I bought it to be quiet, not run an a ton of wattage.
I know there are other PSUs that employ this kind of "passive" fan technology (fan only kicks on when needed) but I can't authoritatively recommend one of them.
Hope this helps! Good luck.