+1 my XFX 750w does the same thing. I think its probably just the fan stopping or something. Either way, its nothing unusual
I don't think it's the fan stopping/starting because the X-series doesn't even turn the fan on until a certain % of load is drawn.
but it's still good to hear that it's nothing to be worried about. I also emailed seasonic and i will try to get back on this post when I receive a reply.