That grinding noise means something is jammed in the main brush module. Hair and string get wrapped around the brush bearings, which restricts rotation and can damage your floors.
Shut it off and flip it over. Open the brush guard by lifting both release tabs. Pull out the main brush and the two flexible side brushes. Remove all hair and debris from the brushes and the bearings. Reinstall the brushes and bearings, then close the guard. Spin the front castor wheel by hand. If it's stiff, pull the wheel out, remove the axle, and clear any debris wrapped around it. Click it back in.
If that didn't work, check the side brush. Use a small screwdriver to remove the screw, pull the brush off, and clear any hair from the housing. Reinstall it.
Heads up: Clean the brushes weekly, or twice a week if you have pets. Replace the main brushes every 6 to 12 months. A clogged front wheel can cause floor damage.