DIAGNOSIS This is coil whine from the monitor's internal power circuitry or backlight inverter. It is an audible vibration of electrical components under load, not a defect that affects image quality.
FIX First, try a different power source. If using a laptop USB-A port for power, switch to a dedicated USB-A wall charger with higher current output (5V/2A or greater). A stable, adequate power supply can sometimes reduce or eliminate the noise.
IF THAT DIDN'T WORK Adjust the screen brightness. Lower the brightness setting via the OSD menu. Coil whine often correlates with power draw; a lower brightness reduces load on the backlight circuit and may stop the noise.
HEADS UP This noise is common in many electronics, including portable monitors. It is not typically a sign of impending failure. If the buzzing is extremely loud or new, it could indicate a failing component, but faint whine is considered normal operation by many manufacturers and is not a warranty issue.