DIAGNOSIS: That's coil whine. It's coming from the power supply board or the local dimming controller circuits. When the TV demands more power for a very bright HDR scene, the electrical components vibrate at a frequency you can hear.
FIX: First, check if it's coming from an external source. Unplug any soundbars or devices connected via HDMI. Play the same bright content (like a snow scene or the sun) and listen. If it's definitely the TV, go to Settings > Picture > Advanced Settings > Local Dimming. Try changing the setting from 'High' to 'Standard' or 'Off'. This reduces the instantaneous power demand on the circuits and can quiet the whine significantly.
IF THAT DIDN'T WORK: If the noise is still unacceptable, it points to a component on the power board that's slightly out of spec. The sound itself isn't a sign of imminent failure, but it is a defect. Contact Hisense support. They are often aware of specific production runs with this issue and may offer a repair or replacement under warranty.
HEADS UP: Don't try to fix coil whine by stuffing foam inside the TV. You'll block critical ventilation and cause the TV to overheat, which will lead to a very real and costly failure.