Many times this is actually caused by various power supplies.
I do know what the noise sounds like, and have heard it on a GIGABYTE board at a friends, but have never heard it on any of my multiple handfuls of boards all using only 1-3 different power supplies. I did test my friends PSU on two of my boards, and then the noise could be heard, so more often than anyone wants to hear, the PSU is the main cause of this issue.