i get a high-pitched whining or grinding noise from my makita impact when i pull the trigger lightly, but it goes away on full power. normal?

Diagnosis

The high-pitched whining or grinding noise occurring specifically during low-trigger engagement on the Makita DTW1002Z is typically caused by "gear chatter" or contamination within the planetary gear reduction system. Because this model uses a brushless motor with electronic speed control, pulling the trigger lightly sends a low-voltage pulse to the motor. At these low RPMs, any microscopic debris, metal slivers from the break-in period, or degraded grease viscosity becomes audible as a rhythmic grind or whine. Once you pull the trigger to full power, the centrifugal force and higher rotational velocity mask the sound and force the gears into a more stable mesh. Another possibility is a slight misalignment or premature wear of the thrust bearings in the anvil assembly. If the noise is accompanied by a slight vibration in the handle, it indicates that the planetary gears are not seating perfectly under low torque, which can lead to premature failure of the gear teeth if not addressed. You can confirm this by running the tool in reverse at low speed; if the pitch of the noise changes or the grinding becomes more pronounced, the issue is mechanical within the gearbox rather than an electrical PWM (Pulse Width Modulation) whine from the controller.

How to Fix It

To resolve this, you need to clear the gear housing of contaminants and ensure the lubricant is properly distributed. Follow these steps precisely:

1. Remove the 18V LXT battery immediately to prevent accidental trigger engagement.
2. Using a high-pressure air compressor with a long-reach nozzle, blast air into the ventilation ports located near the rear of the motor and the front of the gear housing. Focus specifically on the area where the anvil meets the casing to blow out any metallic dust or grit.
3. Cycle the tool through its speed settings (Forward and Reverse) 10-15 times without a load, varying the trigger pressure from a light touch to full throttle. This helps redistribute the factory grease across the planetary gear teeth.
4. If the noise persists, remove the outer casing screws to access the gear assembly. Inspect the planetary gears for "pitting" or silver-colored flakes in the grease.
5. Clean out the old, contaminated grease using a lint-free cloth and a mild solvent.
6. Apply a high-pressure, molybdenum-disulfide (MoS2) rated gear grease. Do not overfill; apply grease to approximately 60% of the gear housing capacity to avoid overheating and "churning" during high-RPM operation.
7. Reassemble the housing, ensuring the O-rings are seated correctly to prevent future debris ingress.

If That Didn't Work

• Replace the Anvil Assembly. If the grinding is localized to the nose of the tool, the internal spring or the hammer pins may be worn. Replacing the anvil unit (the front-most rotating component) often eliminates the noise if the planetary gears themselves are intact.
• Inspect the Brushless Controller. If the noise is a very high-pitched electronic scream rather than a mechanical grind, the PWM controller may be failing. This is rare on the DTW1002Z but can happen if the tool has been subjected to extreme moisture or overheating. This requires a replacement of the electronic control module.
• Check for Bearing Flat-Spots. If the tool was dropped while the anvil was locked, the thrust bearing may have developed a "flat spot." This causes a rhythmic whine at low speeds. You will need to press out the old bearing and press in a new high-grade steel bearing of the exact same dimensions.
• Verify Battery Compatibility. Ensure you are using a genuine Makita 18V LXT battery. Some third-party "knock-off" batteries provide inconsistent voltage/current delivery, which can cause the brushless motor to "stutter" or whine at low trigger pulls.

Heads Up

• Avoid using "WD-40" or thin penetrating oils inside the gearbox; these will strip the heavy-duty grease and lead to total gear failure within a few hours of use.
• Never run the tool "dry" (without grease) even for a short test, as the planetary gears in the DTW1002Z generate immense heat and friction instantly.
• Periodically blow out the motor vents with compressed air every 20-30 hours of heavy use to prevent metallic dust from migrating into the electronics.
• If you notice the noise is accompanied by a smell of burning ozone or hot metal, stop use immediately as this indicates a gear tooth has sheared.