DIAGNOSIS Coil whine from the power supply circuitry or the LCD panel's inverter. It's a physical vibration of inductors or transformers under electrical load.
FIX This is a component-level issue. First, try a different, high-quality power outlet on a different circuit. Sometimes dirty power exacerbates it. In the OSD, try lowering the brightness and contrast from max settings. This changes the electrical load and can reduce or shift the noise frequency.
IF THAT DIDN'T WORK The whine is built into the specific monitor's components. If it's audible over normal room noise, it's a defect. Contact support. The only true fix is a board replacement, as damping the coils requires disassembly and specialized material.
HEADS UP Coil whine is not a safety hazard, but it can be a sign of lower-quality power regulation components. It does not mean the monitor is about to fail.