DIAGNOSIS: You're hearing coil whine from the power supply components, most likely from the local dimming circuitry for the full-array LED backlight. It's a common trait in many LED TVs, especially when displaying very bright scenes or specific color patterns.
FIX: First, let's see if it's tied to a specific setting. Go to Settings > Display & Sound > Picture > Advanced settings > Brightness. Try lowering the Peak Brightness setting from High to Medium or even Low. Also, switch Contrast down a few notches. Play some content and see if the noise reduces. The power draw is less on lower brightness, which often quiets the coils.
IF THAT DIDN'T WORK: Check if it's coming from a specific area. The sound is usually from the center-back of the TV. Make sure all the screws on the back panel are snug (but don't over-tighten!). A slightly loose panel can resonate and amplify an otherwise faint electronic hum.
HEADS UP: This noise can change or get louder in certain picture modes, like Vivid or IMAX Enhanced, because they push brightness and contrast to the max. If it's only audible when you're right up close to the TV and disappears at normal viewing distance, it's generally considered within normal operation and isn't a sign of impending failure.