my roomba 694 is making a horrible grinding noise when it runs, sounds like it's chewing rocks.

Diagnosis

The "chewing rocks" sound in an iRobot Roomba 694 is almost always caused by a foreign object becoming trapped between the rotating rubber extractors and the plastic chassis, or a failure in the gear assembly that drives the main brush module. When a hard object—like a pebble, a small LEGO piece, or a coin—gets sucked up, it can bypass the debris bin and lodge itself directly against the rotating rollers. As the motor attempts to spin the rollers at high RPMs, the object is dragged across the plastic housing, creating a loud, rhythmic grinding or rattling noise. Alternatively, this sound can indicate a "stripped gear" within the brush module. If the Roomba hits a heavy object (like a thick rug fringe or a stray sock) that jams the roller, the plastic teeth of the internal drive gears can shear off. Once the gear is stripped, the motor continues to spin, but the gear slips and chatters against the drive wheel, producing a metallic grinding sound even when no debris is present. You can confirm this by removing the rollers; if the noise persists while the motor is running without the brushes installed, the issue is internal gear failure rather than a foreign object.

How to Fix It

Follow these precise steps to clear the drive system and inspect for damage:

1. Power down the unit by pressing and holding the CLEAN button for 10 seconds until the lights go off. Flip the robot onto its back on a flat, hard surface.
2. Press the release tab on the debris bin and slide it out of the chassis.
3. Locate the two green release tabs on the sides of the main brush module. Press these and lift the entire brush assembly out of the robot.
4. Slide the two green rubber extractors out of their housing. Inspect the ends of the rollers where the plastic caps are located; hair and grit often build up here, creating friction that sounds like grinding. Use a pair of tweezers to remove any trapped debris.
5. Reach your finger into the brush chamber (the cavity where the rollers sit). Feel for any small pebbles or hard plastic shards lodged in the corners or against the drive gear.
6. Inspect the gear teeth on the ends of the rubber rollers. If you see flattened or missing plastic teeth, the rollers must be replaced.
7. Reinsert the rollers, snap the module back into the chassis, and slide the bin back in.
8. Run a short "Spot Clean" cycle to verify the noise has ceased.

If That Didn't Work

• Inspect the Side Brush (Edge-Sweeper): Remove the three small screws holding the side brush in place. Check the gear mount underneath the brush. If a small stone is wedged between the brush head and the robot's body, it will create a high-pitched grinding sound as it rotates.
• Check the Caster Wheel: The front swivel wheel can collect hair and grit in its axle. Pull the caster wheel module out of its socket (it pops out with a firm tug). Clean the axle with a damp cloth and a toothpick. A seized caster wheel causes the robot to "scrub" the floor, which can sound like grinding during turns.
• Replace the Main Brush Module: If the noise persists and you've cleared all debris, the internal drive gear in the module has likely failed. Purchase a replacement Brush Module (Part #694-BM) and swap the entire assembly.
• Check for Motor Bearing Failure: If the grinding is accompanied by a burning smell, the vacuum motor bearings may have failed. This requires a full motor replacement and is typically a sign of the unit being used in an environment with excessive fine dust or moisture.

Heads Up

• Avoid Wet Debris: Never run the 694 on damp floors. Moisture allows grit to paste onto the gear teeth, accelerating wear and causing the "grinding" sound to develop prematurely.
• Weekly Roller Maintenance: Every 7 days, remove the rubber extractors and slide off the end caps. Removing the hair wraps from the ends prevents the rollers from pulling on the drive gears, which prevents gear stripping.
• Clear the Path: Before running a cycle, do a quick "sweep" of the floor for small hard objects like coins or hair ties. The 694 lacks the advanced obstacle avoidance of higher-end models and will attempt to "eat" almost anything smaller than a golf ball.