DIAGNOSIS That's coil whine from the monitor's internal power supply or backlight circuitry. It's an electronic noise, not a fan. It's most noticeable when the monitor is displaying very bright or high-contrast scenes, which changes the electrical load.
FIX First, rule out other sources and try simple power fixes.
- Turn off all other electronics nearby to isolate the sound. It's definitely coming from the back of the monitor.
- Try a different power outlet, preferably on a different circuit. Poor power quality can exacerbate coil whine.
- In the OSD, go to Picture > Brightness and lower it from the default 100. Even dropping to 80 can significantly reduce or eliminate the noise.
- Also try disabling B.I.+ (Brightness Intelligence Plus) in the OSD under Picture, as its constant sensor adjustments can trigger the noise.
IF THAT DIDN'T WORK If the whine is loud and persistent from day one, it may be a component defect. Contact BenQ support while under warranty. They are generally aware this can occur with some units.
HEADS UP This is an annoyance, not typically a sign of impending failure. However, if the noise suddenly changes or is accompanied by a burning smell or visual artifacts, power off immediately.