Get a empty paper towel roll and hold it up to yoru ear while the board is running with CPU installed, and see if you can narrow down the buzz to a certain component or area.
The only way it's going to actually run is if you have the CPU installed, one stick of memory,the 24 pin ATX motherboard cable, and 4 or 8 Pin ATX 12V CPU power cable. If you are missing one of those it is not going to run/start, so no need to test with any of those out of the equation.
I'm sure it's probably just as DM mentioned, coils, which could be the board itself or the PSU. What PSU are you using?
You can test this to be sure that it's coil vibration by doing the following, go into the BIOS and disable C1E and EIST, then the noise should go away.
For the above to work, you may or may not need to update the BIOS, some BIOS are more affected that others.