DIAGNOSIS This is coil whine from the monitor's internal power supply or circuitry. It is often related to the backlight brightness level or the refresh rate being used.
FIX The noise is often most pronounced at specific backlight brightness levels. Adjust the brightness. Open the OSD, go to Picture, and adjust Brightness. Try setting it to 100% or to a very low level like 20%. Often, the whine diminishes at the extremes. If using a high refresh rate like 180Hz (Overclock), try reducing it to 144Hz in the OSD under Game Adjust > Overclock.
IF THAT DIDN'T WORK The whine may be exacerbated by the monitor's power saving features or the specific content being displayed. In the OSD, go to General > Energy Saving and set it to Off. This provides consistent power to the panel. Also, ensure the monitor is plugged directly into a wall outlet, not a power strip with other high-draw devices.
HEADS UP Coil whine is not typically a sign of imminent failure but can be a nuisance. It is more common in units with high refresh rate Nano IPS panels. If the noise is severe and changes with the on-screen content, it is a characteristic of the specific unit's components. Contact LG support if the noise is intolerable, as some units are quieter than others.