DIAGNOSIS This is coil whine from the power supply circuitry. It is a physical phenomenon, not a defect in the panel. The sound occurs during high brightness, high-contrast scenes because the power regulation components vibrate at an audible frequency.
FIX First, disable any automatic brightness features that may be causing rapid power fluctuations. Go to Settings > Display & Sound > Picture > Brightness. Set Light Sensor to Off. Then, go to Picture > Advanced Settings > Brightness. Set Peak Luminance to Medium or Low. This reduces the maximum power draw and often eliminates the whine.
IF THAT DIDN'T WORK The whine may be more noticeable in a very quiet room due to specific AC power conditions. Try plugging the TV directly into a wall outlet, not a power strip or surge protector. Ensure the outlet is grounded. Power cycle the TV by unplugging it from the wall for two full minutes.
HEADS UP This sound does not indicate impending failure and does not affect picture quality or lifespan. It is a common characteristic of the power design in many OLED TVs, including this model. If the sound becomes a loud buzz or crackle, contact Sony support.