roomba j7+ is making a horrible grinding noise only when it's on carpet, sounds awful.

Diagnosis

The grinding noise occurring specifically on carpet is almost always caused by "end-cap friction" or "axle binding." When the Roomba j7+ transitions from hard floors to carpet, the drive motor increases torque to push the dual multi-surface rubber brushes through the pile. If hair, long threads, or carpet fibers have wound tightly around the ends of the rubber brushes, they create a dense, hardened ring of debris that presses against the plastic housing of the brush modules. This creates a mechanical conflict where the brush is trying to rotate, but the accumulated debris is rubbing against the internal chassis, resulting in a loud, rhythmic grinding or screeching sound. Because carpets provide more resistance than hard floors, the motor strains harder, amplifying the noise. You can confirm this by flipping the robot over and attempting to spin the rubber brushes by hand; if they feel stiff or "springy" rather than rotating freely, you have an accumulation problem.

How to Fix It

To eliminate the grinding noise, you must perform a deep clean of the brush modules and the drive axles. Follow these exact steps:

1. Power down the robot completely by pressing and holding the CLEAN button until the light ring goes dark.
2. Flip the robot onto its back on a soft surface to avoid scratching the top sensor array.
3. Locate the two green release tabs on the brush module frame. Press these tabs to pop open the brush bin.
4. Lift out both rubber brushes. Note that the j7+ uses two counter-rotating brushes; keep track of which is left and which is right.
5. Pull the plastic end-caps (the small removable caps at the ends of each brush) off. This is where 90% of the debris hides.
6. Use a pair of small embroidery scissors or a seam ripper to cut through the hair and carpet fibers wrapped around the brush axle. Do not pull the hair out forcefully, as this can warp the rubber brush.
7. Check the interior of the brush modules (the plastic housing). Use a can of compressed air or a vacuum hose to remove any grit or pebbles trapped in the gear teeth.
8. Inspect the brush bristles for any melted rubber or embedded shards of plastic that might be scraping the chassis.
9. Slide the brushes back into their slots, ensuring the end-caps are snapped firmly back into place, and lock the green frame.

If That Didn't Work

• Inspect the Side-Sweeping Brush: Remove the single screw holding the side brush in place using a Phillips head screwdriver. Check for hair wrapped around the gear axle beneath the brush. If the brush is worn down or the axle is bent, the bristles may be slapping the carpet at high speeds, creating a rattling or grinding sound.
• Check the Caster Wheel: Pull the front omni-wheel (the small swivel wheel) straight up and out of its socket. Check for "hair donuts" wrapped around the axle of the wheel. If the wheel cannot swivel freely, it will drag across the carpet, creating a high-pitched scraping noise.
• Examine the Drive Wheels: Press the release buttons on the two main drive wheels to remove them. Check for any debris caught between the wheel and the robot's body. A small pebble trapped here will grind against the carpet fibers during every rotation.
• Replace the Rubber Brushes: If the rubber fins on the brushes are torn or have "mushroomed" (expanded due to heat/wear), they will rub against the internal guard. Replace the brushes with a genuine iRobot j7 replacement set (Part # 4550).

Heads Up

• Weekly Maintenance: To prevent this noise from returning, remove the brush end-caps once a week. Hair builds up inside the caps even if the brushes look clean from the outside.
• Avoid Wet Cleaning: Never use liquid cleaners on the rubber brushes or the drive axles, as this can strip the factory lubrication from the plastic gears, leading to permanent grinding.
• Check for "Hair-Tangles": If you have long-haired pets, check the brush modules every 3-4 cycles. The j7+ is efficient, but dense fur can compress into a hard plastic-like ring that can eventually crack the brush module frame.
• Clear the Path: Ensure there are no loose threads or frayed edges on your carpets, as the j7+ brushes are designed to grip, which means they will actively "pull" loose carpet fibers into the axles.