I agree, it sounds like an issue with a coil whine. It is likely your Power Supply. I would definitely check there first. If you could mount your power supply outside of your case or run it with a panel removed and put it under a pretty decent load, listen around your power supply and see if it is coming from there. The sound will come from the openings, so be sure to pay attention to the fan opening (in case it is mounted upside down) or the back.