Not to be funny, but that's some pretty good "guess work" without system specs listed. I say that because there was an issue with certain motherboards and power supplies causing coil hum. In fact, one power supply company wound up replacing the offending power supplies.
System specs would help tremendously here.
My two cents.
OP's system spec listing...
System Manufacturer/Model Number have several computers, not just one
OS Windows 7 64-bit
Sorry, just trying to help.
Thanks Sygnus, honestly this same topic has come and gone so many times at the EVGA forum that I lost count. It's also been confirmed that the coils on the MB are responsible for making the noise although the power supply is the actual culprit. Although changing the MB has also fixed this problem on occasion. No system specs required for me to figure this one out LOL.
As you summized and suggested, the only fix seems to using a different or higher out power supply or changing out the MB. This has been confirmed to work quite a few times already.

My Computer
At a glance
Windows 7 Ult, Windows 8.1 Pro,Q9650-4.275GHz, E8600 4.5GHz, E6750-3.8GHzG.Skill PC2 9600 1200Mhz 5 5 5 15 2TGTX480
- Computer type
- PC/Desktop
- Computer Manufacturer/Model Number
- Home built
- OS
- Windows 7 Ult, Windows 8.1 Pro,
- CPU
- Q9650-4.275GHz, E8600 4.5GHz, E6750-3.8GHz
- Motherboard
- Evga 780i FTW
- Memory
- G.Skill PC2 9600 1200Mhz 5 5 5 15 2T
- Graphics Card(s)
- GTX480
- Sound Card
- Asus Xonar D2
- Monitor(s) Displays
- HannsG
- Screen Resolution
- 1680X1050
- Hard Drives
- GSkill Phoenix Pro 120GB SSD
- PSU
- ThermalTake Toughpower 1000Watt modular
- Case
- ThermalTake XaserV
- Cooling
- Xigmatek S1283
- Keyboard
- Logitech G15
- Mouse
- Logitech G9
- Internet Speed
- T1