Diagnosis
That is coil whine from the monitor's internal power supply or display drivers. It's an electrical noise caused by components vibrating under high load. Brighter, high-motion scenes draw more power.
How to Fix It
First, enable Eco Mode in the OSD under System. This reduces peak power draw. If that doesn't help, lower the monitor's brightness and refresh rate from the maximum setting. This reduces electrical stress on the components causing the noise.
If That Didn't Work
The whine may be excessive. Contact Samsung support. Persistent, loud coil whine can be grounds for a warranty replacement, but you must demonstrate it clearly in a quiet room.
Heads Up
This noise is generally not a sign of impending failure, just an annoyance. Do not open the monitor to try to fix it. You will void the warranty and risk electric shock.