DIAGNOSIS That's almost certainly a damaged side brush. One of the arms has snapped off or is hitting the floor because its mount is cracked or wobbly.
FIX Stop the robot and flip it over. Identify which side brush is making the noise. Remove it by unscrewing the single Phillips-head screw in the center. Inspect the plastic arms for breaks and the gear underneath for debris. Replace the side brush with a new one (they're cheap and sold in multipacks). Make sure it's screwed on snugly, but don't overtighten.
IF THAT DIDN'T WORK The noise could be from the wheel assembly on that side. Check for a large object (like a Lego, hair tie, or gravel) stuck in the wheel tread or jammed in the wheel suspension pivot point. Manually spin the wheel to feel for grit or binding.
HEADS UP The cloth anti-tangle side brushes that sometimes come with the Q7 Max are less durable than the standard stiff ones. If you have those, consider switching back to the standard type.