I've noticed that my Corsair GS700 in the rig I recently built will occasionally make a buzzing noise, especially when playing a game. After researching online, it sounded like it was possibly coil whine, but when I looked that up on youtube it wasn't the same noise. Then I found this video and this is exactly the noise that I'm hearing.
I found a posting (in a foreign language. thank you google translator) that if the fan is put in upside down that it'll make that noise. I flipped it up and I haven't had the issue so far... Hopefully that fixed it for good. I guess I just won't have use of my nifty dust screen on the bottom of my case. Will it make my PC hotter by having the fan face inside of the case instead of out?
The fact that it buzzes when it's oriented with the fan facing downward is a defect.
With the fan facing toward the inside of the case you will be drawing warm case air through the PSU instead of the cooler outside air. Air flow through the case will also be affected.
If you're using two graphics cards in CrossFire or SLI the secondary graphics card will most likely be situated close to the power supply if your power supply is mounted at the bottom of your case. With the PSU's fan facing upward both the PSU and the secondary graphics card will both be fighting each other for cooling air.