They are, and are supposedly good design and good components:
- Not only this design proved to be superior, but Corsair/CWT decided to use only high-end components inside this unit, which features only Japanese capacitors and solid caps on the DC-DC converters in charge of the + 5 V and +3.3 V outputs. Voltage stability was another highlight, with all voltages within 3% from their nominal values, i.e., we saw voltages closer to their nominal values than what allowed by the ATX standard, which specifies a 5% tolerance (10% for -12 V). We could also pull up to 1,000 W at 57º C from this unit, which is really impressive.
http://www.hardwaresecrets.com/article/Corsair-HX850W-Power-Supply-Review/741/10
But that doesn't mean they have properly glued down loose components or used special components to combat electrical noise/coil whine/capacitor resonance. Hmm it seems to be hit and miss and a combination of components, even CPU+motherboard can make the psu whine, not just gpu. MSI have actually done something about that, but no recent graphics cards from them have gotten same treatment:
- MSI's new chokes and power design to stop the Nvidia GTX 260 and 275 from squealing.
http://www.bit-tech.net/news/hardware/2009/05/29/msi-solves-the-nvidia-gtx-squealing-problem/