There are several things the buzzing could be, not just capacitors, however none are fixable unless you are an electronics technician.
Cheaper Power Supplies tend to have these issues more often. They also likely don't fall under Warranty reasons to return it either.
I'm not sure who said "all Corsair PSU's are good" but that's simply not true. The company makes expensive high-end models and low-end models that are more prone to have issues. My Corsair PSU just blew up on me (CX430) after 30 minutes so I bought an Antec VP-450 in that instance to replace it.
**Long story short, you need to buy a different Power Supply likely. Preferably one with a minimum of 30 comments and high average review AND no complaints about buzzing.