the mop washing base makes a loud grinding noise when it scrubs the mop pads.

Diagnosis

The loud grinding noise during the mop washing cycle on the Roborock S8 MaxV Ultra is typically caused by foreign debris—specifically long hair, synthetic threads, or coarse sand—becoming lodged between the rotating scrubber brush and the drive axle of the washing module. Because the scrubber operates at a high RPM to frictionally clean the mop pads, even a small amount of grit can create a resonant vibration or a physical obstruction that forces the motor to struggle, resulting in a metallic or plastic grinding sound. You can confirm this by listening closely to the base during the "Mop Washing" phase of the dock cycle. If the noise is rhythmic and coincides exactly with the rotation of the scrubbing mechanism, it is a mechanical obstruction. If the noise is accompanied by a "Mop Washing Failed" error on the app or a blinking red light on the dock, the motor is likely experiencing too much torque resistance from a jam, triggering a safety shut-off to prevent the gearbox from overheating.

How to Fix It

To resolve the grinding noise, you must perform a deep clean of the scrubbing assembly. Follow these exact steps:

1. Power down the dock completely by unplugging it from the wall outlet to prevent the scrubber from activating while your fingers are in the mechanism.
2. Remove the water tank and the waste water tank to clear the workspace.
3. Locate the removable washing plate (the plastic tray where the robot parks to have its mops cleaned). Gently lift the plate upward and out of its seated position.
4. Inspect the rotating nylon scrubber brush located beneath the plate. Look for "hair rings"—tightly wound bundles of hair—around the center axle and the end caps of the brush.
5. Use a pair of fine-tipped tweezers or a seam ripper to carefully cut through and pull out any wound debris. Be sure to clear the gap between the brush head and the motor housing.
6. Use a vacuum or a can of compressed air to blow out any sand or grit trapped in the gear teeth of the drive axle.
7. Manually rotate the scrubber brush with your hand; it should spin smoothly with slight resistance but no "clicking" or "grinding" feel.
8. Reinstall the washing plate, ensuring it clicks firmly into place, and plug the dock back in.

If That Didn't Work

• Gearbox Failure: If the noise persists despite a clean brush, the internal plastic gears within the washing module have likely stripped. This manifests as a high-pitched grinding sound even without a load. In this case, the entire wash module assembly (the internal motor and gear housing) must be replaced as it is a sealed unit.
• Bearing Wear: Check if the scrubber brush is wobbling on its axis. If the bearing has worn out, the brush will tilt during rotation, causing the nylon bristles to rub against the plastic housing of the dock. Replace the nylon scrubber brush component.
• Water Pump Interference: Occasionally, the noise is not the scrubber but the water pump struggling due to an air lock or a partial blockage in the feed line. Try running a "Self-Clean" cycle via the app to flush the system with high-pressure water.
• Base Leveling: Ensure the dock is on a completely flat surface. If the dock is tilted, the scrubber brush may be pressing unevenly against the mop pads, creating excessive friction and a grinding sound. Use a spirit level to verify the dock is plumb.

Heads Up

• Never ignore a grinding noise during the wash cycle; continuing to operate the dock with an obstruction can shear the plastic gear teeth, turning a simple cleaning task into a costly hardware replacement.
• Avoid using thick, third-party aftermarket mop pads that are denser than the original Roborock pads, as these increase the torque load on the scrubber motor and accelerate wear.
• Clean the washing plate and the scrubber brush every two weeks to prevent the buildup of "sludge" (a mix of hair and cleaning solution) which can harden and jam the mechanism.
• Ensure you are using the official Roborock cleaning solution; using high-viscosity soaps can leave a sticky residue on the axle, attracting more debris and increasing friction.