its a tad louder than a my old 235w PSU which really was litterally silent. It actually sounds like a bit like the insects called 'crickets' when its the only noise you can hear. But, the important point is that every other fan will be louder. The noisiest is still my northbridge HSF - fast and sh!te.
edit: not to forget it has TWO fans, so if you want to make it even quieter you can diable one of them.