I have a brand new M3A770DE, and the CPU is AMD Athlon II X4 640
When on full load (prime95) something is buzzing on the mobo. And it really can be heard.

Except that, when my graphic card goes to idle (157 MHz core and 300 MHz memory) and lowers its voltages, there is some higher pitched noise, but I can't be sure that it's from the graphic card or mobo. This was happening on my older mobo as well so maybe this is GPU-s fault. However, I've put some older card instead of this one, and the problem with CPU full load still remains.

I've noticed another thing as well. All the settings are on default, the CPU vcore voltage shows as 1.36V in sensor reading in BIOS, while in Windows, using CPU-Z or SpeedFan, the sensor for vcore reads 1.44 up to even 1.448V when on full load!
The power supply is Corsair CX400, 400W

The system is stable under full load, I've left it for a few hours doing Prime95 and there were no errors....

Is there some solution for this buzzing sound? It's very irritating. I've bought this new mobo as a replacement for my old ASRock AliveXfire-esata2 which I've had for over 4 years, and I thought it had started to die because of the problems with graphic card idle mode and strange flickering of the screen while in idle mode, but there problems have continued through to this new mobo, so I've bought this new mobo for nothing. I'm tempted to go back to the old mobo since that one didn't have this damn buzzing when CPU on full load.... but I can't return this new one because it's obviously not broken (as it works stable), just very noisy :(