Yeah, this one's common. You've almost certainly got a rock, stick, or a wad of packed grass jammed under the deck, hitting the blade. Stop immediately.
- Turn the mower off and remove the battery.
- Tip the mower on its side, with the air filter and carburetor (if it had one) facing UP. For this electric mower, just make sure the side with the battery port and controls is up.
- Clear all debris from the blade area and the underside of the deck. Use a stick or brush, not your hands.
- Check the blade itself for damage like bends or nicks. A damaged blade needs replacement before you run it again.
IF THAT DIDN'T WORK: If the noise persists with a clear deck and undamaged blade, the motor bearings or blade adapter could be failing. That's a service center job.
HEADS UP: Always clear the mowing area of loose stones, toys, and wire before you start. They're the main culprits for this noise and can ruin your blade or deck.