DIAGNOSIS That's likely coil whine from the internal power supply or components. It's an annoying but common issue with many LCD monitors, not unique to this model, and often related to the backlight intensity.
FIX First, try adjusting the monitor's brightness. Lower it from 100% to 70-80% and see if the noise diminishes. Often, the whine is most pronounced at maximum brightness. Also, ensure the monitor is plugged directly into a wall outlet, not a power strip or surge protector that might be introducing electrical noise.
IF THAT DIDN'T WORK Try a different power cable if you have a compatible one. Sometimes the cable itself can be a factor. If the noise is truly unbearable and present from day one, it could be a component defect. Coil whine is generally not covered under warranty unless it's exceptionally loud, but contacting Dell support is an option.
HEADS UP The noise can change or get louder based on what's on screen. A fully white webpage will often cause more whine than a dark movie scene. It's a physical characteristic, not a sign of imminent failure.