I have the same issue.
My system is i7 920, GIGABYTE EX58-UD3R, Nvidia GIGABYTE 560Ti
PSU is new Thermaltake 675W 80 Bronze
After some tests and playing with components I think the trouble maker is the motherboard. Because PSU is not whistling with other systems.
There are many options that I've found:
1. Update your motherboard bios
2. Disable in bios C1E (CPU Advanced) function
3. Disable in bios all power energy saving options