I've had a similar problem. My previous system was a C2D@3GHz on a Gigabyte board. The PSU was a Corsair HX520. When I upgraded the mobo, CPU and RAM, the PSU started emitting a very high frequency tone. It sounded like an old CRT TV being on in another room. To make matters worse, I was the only one hearing it and it was driving me mad. I've tried toying around with C1 states and over voltage but nothing helped. I even opened the PSU, voiding the remaining two years warranty, and put some hot glue on the coils...
...minor improvement, not worth it really.
Then I began swapping PSUs around. I tried connecting a Corsair VX430 from another machine but it had exactly the same piercing tone. Then I tried my brother's CoolerMaster SilentPro 500W and voila, that was it! There's still some sizzle of electricity from up close, but the tone is gone and the PC is as good as silent from where I sit
Interestingly, the old HX520 works now in my brother's computer... and it's inaudible! So I'd say it boils down to particular setups and the way specific components task the PSU's circuitry. Also, we both have an i5 2500K and overclocked, and it's now known to make 3 different models of PSUs whine - there might be a rule here.