my roomba i3+ is making a horrible grinding noise from the bottom, what do i check?

Diagnosis

The grinding noise emanating from the bottom of an iRobot Roomba i3+ is almost always caused by a mechanical obstruction in the drive wheels or the dual multi-surface rubber brushes. When a foreign object—such as a piece of plastic, a pebble, or a tightly wound clump of hair—gets lodged in the gear assembly or the brush bearings, it creates high friction. As the motors attempt to force the rotation, the gears "slip" or grind against one another, producing a loud, jarring metallic or plastic rattling sound. Alternatively, the noise may stem from a failed bearing in one of the two main drive wheels. If the internal axle of the wheel has worn down or a piece of debris has entered the wheel housing, the wheel will wobble during rotation, causing the plastic chassis to rub against the drive mechanism. You can confirm the source by lifting the robot and manually rotating the wheels and brushes; if one resists movement or makes a clicking sound while the others spin freely, you have located the failure point.

How to Fix It

Follow these steps to isolate and remove the obstruction:

1. Power down the Roomba i3+ completely by pressing and holding the Clean button until the light ring turns off.
2. Flip the robot over onto a flat, clean surface.
3. Remove the two green multi-surface rubber brushes. Press the gray tabs to release them from their housings.
4. Inspect the brush ends. Slide off the yellow hair guards (the small plastic caps at the ends of the rollers) and remove any hair or string wrapped around the axles.
5. Check the brush modules themselves. Use a flashlight to look inside the brush housing for small pebbles or hard debris that may have bypassed the brushes and entered the gear housing.
6. Inspect the main drive wheels. Gently press the wheel into the chassis and pull it back out to ensure the spring-loaded suspension is working. Rotate each wheel manually by hand; it should spin smoothly without any "catching" or grinding sensations.
7. Clean the side-brush (the small spinning brush). Pull the screw out of the center of the side brush and remove the brush entirely to check for hair wrapped around the motor pin.
8. Reinstall all components, ensuring the rubber brushes are snapped firmly into place and the yellow caps are secure.

If That Didn't Work

• Replace the Main Drive Wheel: If the grinding persists and is isolated to one wheel, the internal gear has likely stripped. You will need to replace the drive wheel module. This involves removing the screws from the underside of the chassis to access the wheel assembly.
• Clear the Vacuum Path: Sometimes the grinding noise is actually the vacuum motor struggling because the extraction path to the Clean Base is blocked. Check the bin for a jammed piece of cardboard or a large clump of debris that is vibrating against the motor housing during operation.
• Inspect the Caster Wheel: Remove the small front swivel wheel. Debris trapped in the caster axle can cause a rhythmic grinding sound as the robot steers. Clean the axle with compressed air and a cotton swab.
• Factory Reset: In rare cases, a sensor error can cause the wheels to "stutter" (rapidly accelerate and decelerate), which sounds like grinding. Perform a hard reset by holding the Clean button for 20 seconds until the light ring swirls.

Heads Up

• Never use lubricants like WD-40 or silicone spray on the rubber brushes or drive wheels; this will attract more hair and grit, leading to permanent gear failure.
• Check your rubber brushes every two weeks. If the bristles or the rubber edges are frayed, they can wrap around the axle and cause the motor to overheat.
• Avoid vacuuming over loose charging cables or thin rugs with long tassels, as these are the primary causes of axle-wrap that leads to grinding noises.
• Ensure the Clean Base is on a hard surface. If the base is on a thick rug, the robot may struggle to dock, causing the wheels to grind against the carpet while trying to enter the charging port.