DIAGNOSIS Coil whine from the power supply components. Common under high brightness/contrast loads.
FIX Reduce the monitor's brightness and contrast. Press the menu button. Go to Picture > Brightness and Contrast. Lower both by 10-15 points. The noise should diminish or stop.
IF THAT DIDN'T WORK Disable any dynamic contrast features. Go to Picture > Advanced > Dynamic Contrast. Set it to Off. Also disable Brightness Stabilizer.
HEADS UP Coil whine is not a defect that affects lifespan. It is an acoustic resonance. If it's loud at normal settings, contact BenQ support. The power supply may be faulty.