DIAGNOSIS Normal operation for a brushless motor drill. The sound is the pulse-width modulation (PWM) from the electronic speed controller sending power in rapid pulses for low-speed control.
FIX No fix needed—this is by design. To confirm it's not a problem:
- Pull the trigger fully. The whining should stop and be replaced by the normal motor sound as the drill reaches full speed.
- If the whining continues at full trigger pull or the drill doesn't spin, then you have an electronic fault.
IF THAT DIDN'T WORK If the sound is a grinding or scraping noise, not a clean electronic whine, the planetary gearset may have a damaged tooth. This requires gearbox inspection.
HEADS UP This sound is most noticeable in quiet environments. It's not a sign of impending failure. Don't confuse it with a continuous beep, which would indicate an electronic fault code.