the auto-empty dock sounds like it's grinding and doesn't suck all the dust out of the robot bin.

Diagnosis

The grinding noise emanating from the Roborock S8 Pro Ultra dock is typically caused by "motor strain," where the high-powered suction motor is attempting to pull a vacuum against a physical obstruction. When the airflow is restricted, the motor's RPMs fluctuate violently, creating a mechanical rattling or grinding sound. This is rarely a sign of a failed motor, but rather a symptom of a pressure imbalance. The failure to empty the robot bin is usually due to a "bridge" of debris—typically a clump of pet hair, a piece of cardboard, or a large seed—that has become lodged in the narrow throat of the robot's dustbin or the dock's suction intake. If the debris is stuck at the interface where the robot meets the dock, the vacuum cannot create a seal, causing the motor to spin without moving air, which produces that characteristic grinding noise. Alternatively, a saturated or improperly seated dust bag in the dock can restrict airflow enough to trigger this sound while leaving the robot bin half-full.

How to Fix It

Follow these steps precisely to clear the airflow path and restore suction:

1. Manually remove the S8 Pro Ultra from the Ultra Dock. Open the robot's rear lid and slide out the internal dustbin.
2. Inspect the dustbin's exit port (the rectangular opening). Use a flashlight to look for compacted hair or debris. Use a pair of tweezers or a thin pipe cleaner to clear any obstructions from the port.
3. Examine the dock's suction intake—the hole where the robot's bin aligns. Reach inside with a finger or a vacuum hose to ensure no large debris has fallen into the throat of the dock.
4. Open the dock's dust bag compartment. Remove the current dust bag. Even if it doesn't feel heavy, check the cardboard mounting flange. If the flange is bent or not seated perfectly flush against the intake port, air will leak, reducing suction power.
5. Inspect the internal airway between the dock's intake and the bag. If you see a buildup of fine dust "cakes" on the plastic walls, wipe them clean with a damp cloth.
6. Insert a fresh, genuine Roborock dust bag, ensuring the plastic collar clicks firmly into place.
7. Place the robot back on the dock and trigger a manual "Empty Dustbin" command via the Roborock app to verify the grinding noise has ceased.

If That Didn't Work

• Check the Dustbin Flap: Inspect the rubber seal/flap on the robot's internal dustbin. If the rubber is warped or has a piece of grit stuck in it, the dock cannot create a vacuum seal. Clean the rubber edge with a microfiber cloth and isopropyl alcohol to ensure a tight fit.
• Clear the Main Brush Roll: A heavily tangled main brush can push debris backward into the bin in a way that creates "clumps" too large for the dock to suck out. Remove the brush roll, cut away all hair wraps from the ends, and reinstall.
• Inspect the Dock's HEPA Filter: The dock has a small exhaust filter. If this filter is clogged with fine dust, the motor will struggle to push air out, causing the motor to overheat and make a loud, strained noise. Gently tap the filter against a hard surface to knock out the dust.
• Hard Reset the Dock: Unplug the Ultra Dock from the wall outlet for 60 seconds. This resets the motor controller and clears any temporary software glitches that might be causing the motor to cycle incorrectly.

Heads Up

• Bag Replacement: Do not wait for the app to tell you the bag is full. If you have high-shedding pets, replace the dock bag every 2 months regardless of the "fill" level to maintain maximum airflow.
• Avoid Wet Debris: Never allow the robot to suck up liquid or damp debris. Wet dust creates a "mud" consistency that hardens in the dock's throat, which is the primary cause of permanent suction loss and motor grinding.
• Generic Bag Warning: Be cautious with third-party "compatible" bags. If the cardboard fitting is off by even 1mm, it creates an air leak that significantly reduces the emptying efficiency.
• Regular Bin Cleaning: Every 30 days, wash the robot's internal dustbin with soap and water. Ensure it is 100% dry before reinserting, as any moisture will cause dust to clump and block the emptying port.