router makes a loud high-pitched whine or screech only at certain speeds, not all the time.

Diagnosis

The high-pitched whine or screeching sound occurring at specific RPM settings on the DeWalt DCW600B is caused by harmonic resonance. This happens when the rotational frequency of the motor armature and the internal cooling fan aligns perfectly with the natural resonant frequency of the tool's plastic housing or the internal mounting brackets. Essentially, the vibrations are amplified by the chassis, turning the outer shell into a speaker for the motor's internal frequency. You can confirm this is a resonance issue rather than a mechanical failure by observing the speed dial. If the noise peaks sharply at a specific setting (for example, exactly at speed 4) but disappears or changes tone significantly when you move the dial just a fraction of a millimeter in either direction, it is harmonic. If the noise were caused by a failing bearing or a bent collet, the sound would typically increase linearly with speed or remain constant regardless of minor adjustments. Another contributing factor can be the interaction between the motor's electromagnetic field and the metal components of the housing. At specific voltages provided by the electronic speed controller, the "singing" effect is intensified, which is a common characteristic of brushless motors and high-efficiency electronic speed controls found in the XR line.

How to Fix It

Since this is a physics-based resonance issue rather than a broken part, the solution involves shifting the operating frequency away from the resonance peak.

1. Power on the router without a bit installed to isolate the motor noise from the cutting noise.
2. Slowly rotate the speed dial from 1 to 6. Identify the exact point where the screeching is loudest.
3. Once the peak noise is found, move the dial slightly (approximately 2-5%) in either direction. For example, if the whine is loudest at the "4" mark, shift the dial slightly toward the "5" or back toward the "3".
4. Test the tool under load with your workpiece. The added resistance of the cut often changes the motor's RPM slightly, which may naturally push the tool out of the resonance zone.
5. If the noise persists during a specific cut, adjust your feed rate. Increasing the pressure slightly can alter the motor load and shift the frequency enough to silence the whine.

If That Didn't Work

• Check for debris buildup in the motor vents. Use compressed air to blow out the cooling ports located at the top and rear of the tool. A partial blockage in the cooling fan shroud can create an aerodynamic "whistle" that mimics harmonic resonance, specifically at higher speeds where air velocity is greatest.
• Inspect the collet and bit seating. A bit that is not seated fully or a collet with accumulated sawdust can cause an imbalance. This imbalance creates a centrifugal vibration that triggers the housing resonance. Remove the collet nut, clean the interior of the collet with a solvent, and re-seat the bit precisely 1/8" to 1/4" from the bottom of the collet.
• Verify the battery seating. Ensure the 20V Max battery is clicked firmly into place. A slightly loose battery can act as a secondary vibrating mass, amplifying the motor's frequency. Remove the battery and clear any dust from the gold-plated terminals before re-inserting it with a firm snap.
• Check for housing cracks. Inspect the plastic casing near the handle and the base assembly. A hairline crack in the polymer housing can create a "reed" effect, where air or vibration causes the crack to flutter at high frequencies, producing a loud screech. If a crack is found, the housing must be replaced to restore structural rigidity.

Heads Up

• Avoid running the router at the resonance peak for extended periods; while not immediately damaging, the sustained vibration can lead to premature wear on the internal motor brushes or bearing races.
• Always use a vacuum attachment when possible. Sawdust infiltrating the motor housing can change the weight distribution of the internal fan, potentially shifting the resonance point or causing overheating.
• Never use "shim" methods (like taping the housing) to dampen the noise, as this can block critical airflow vents and lead to thermal shutdown of the brushless controller.
• Periodically check the tightness of the base plate screws. If the base is slightly loose, it can act as a tuning fork, amplifying the motor's high-pitched whine through the workbench.