Do not buy the Corsair HX650 80+ Gold. It has a major problem. When I played games or did any 3d modelling it made a whistling or chirping noise. My replacement unit did the same thing. I looked up the reviews online on amazon and everyone there was having the same problem. This means there's a problem in design. I bought it simply on the brand name, wattage and 7 year warranty.
As amuffin said, it's probably coil whine. It's hateful but norm around any components.
As many people here said, Corsair's HX and AX series are their premium models. It's possible that most personal customer reviewers just had some bad units (it happens to everything) or as bignastyid said, some people are overloading the units. Anyway, the point is that you have nothing to be extremely worried about.