DIAGNOSIS: That's an electrical ground loop or interference from a nearby component, often coming through the internal amplifier. It's especially noticeable because the speakers are small and the cabinet is thin.
FIX: First, unplug all external devices (HDMI, optical, even USB). Just have the TV on power alone. If the buzz stops, you've found the source. Plug devices back in one by one. The most common culprits are cable/satellite boxes, soundbars using optical, or gaming consoles. For the guilty device, try a different power outlet or a different HDMI cable.
IF THAT DIDN'T WORK: Go to Settings > Sound > Expert Settings and turn off 'Adaptive Sound' and any 'Voice Enhancement' features. These can amplify electronic noise. Also, ensure the TV's firmware is updated, as audio driver updates sometimes address this.
HEADS UP: If the buzz is still there with everything unplugged and is coming from the back of the TV (not the speakers), it could be coil whine from the power supply. This is a hardware issue, but it's usually harmless, just annoying. Contacting Samsung support is the next step if it's loud.