it's making a loud grinding or rattling noise from one side when it drives, but vacuums fine.

Diagnosis

The loud grinding or rattling noise occurring specifically during movement—while the vacuum suction remains functional—indicates a mechanical failure in the side brush assembly or the drive wheel train. In the Roborock Q7 Max, this is most commonly caused by a "stripped" side brush gear or a foreign object (like a small pebble or a piece of hard plastic) lodged between the side brush hub and the chassis. Because the noise is rhythmic and tied to the driving speed, it is likely that the plastic bristles of the side brush have worn down or the central mounting screw has loosened, causing the brush to wobble and strike the underside of the robot's plastic casing. Alternatively, if the noise is a deeper, metallic grinding, the issue is likely a "wheel jam" where hair or carpet fibers have wound themselves tightly around the axle of one of the two main drive wheels. This creates friction against the internal motor housing. You can confirm this by placing the robot on a flat surface and gently pushing it backward; if one wheel resists more than the other or makes a clicking sound, the drive gear is fouled. If the noise only happens when the side brush is spinning, the failure is located in the side brush motor's planetary gear set.

How to Fix It

Follow these steps to isolate and resolve the noise:

1. Power down the Roborock Q7 Max completely using the power button on the top of the unit to prevent accidental motor engagement.
2. Flip the robot over onto a soft surface to avoid scratching the LiDAR turret.
3. Locate the side brush making the noise. Use a Phillips #2 screwdriver to remove the single center screw. Lift the side brush assembly off the hub.
4. Inspect the white plastic drive gear (the hexagonal peg) protruding from the chassis. If the edges of this peg are rounded off or "stripped," the brush will slip and rattle. If it is intact, check for hair wrapped around the base of the gear and remove it using tweezers.
5. Inspect the side brush itself. Look for any cracks in the plastic arms or missing bristles that could be causing an imbalance. If the brush is warped, replace it with a genuine Roborock replacement part.
6. If the side brush is clear, inspect the main drive wheels. Grab the rubber tire and pull it slightly outward from the chassis. Use a needle-nose plier to pull out any hair or string wound around the axle.
7. Reinstall the side brush, ensuring the screw is tightened firmly but not over-torqued, as the plastic housing can crack.
8. Place the robot back on the floor and run a "Spot Clean" to verify the noise has ceased.

If That Didn't Work

• Replace the Side Brush Motor: If the grinding persists even with the brush removed, the internal planetary gears of the side brush motor have likely failed. This requires opening the chassis to replace the small DC motor assembly. This is common if the robot has frequently collided with heavy furniture while the brush was pinned.
• Check the Front Caster Wheel: A rattling noise can often be mistaken for a side brush issue when it is actually the omni-directional front wheel. Pop the caster wheel out of its socket using a flat-head screwdriver and remove the internal axle. Clean out the compacted "hair donut" that forms around the axle, as this causes the wheel to vibrate violently.
• Inspect the Main Brush Bearings: While you mentioned it vacuums fine, a partially seized bearing on the main roller brush can create a resonance that sounds like it's coming from the side. Remove the main brush and check the square drive end; if the plastic is melted or worn, the vibration will travel through the chassis.
• Calibrate the Drive Wheels: If the noise is accompanied by the robot veering to one side, there may be a misalignment in the drive gear. Ensure the rubber treads are clean of oil or grease, which can cause the wheels to slip and "chatter" against the floor.

Heads Up

• Avoid Generic Brushes: Cheap third-party side brushes often have slightly different diameters or harder plastics that can put undue stress on the side motor, leading to the very grinding noise you are experiencing.
• Weekly Caster Cleaning: The front caster wheel is a magnet for hair. Pop it out once a week to prevent the axle from seizing, which protects the drive motors from overworking.
• Screw Tension: Never over-tighten the side brush screw. The plastic mount is thin, and stripping the threads will require a full chassis replacement.
• Debris Check: If you have a pet that sheds heavily, check the drive wheel gaps every two weeks. Compacted fur can act like a wedge, pushing the gear out of alignment.