Yeah, this one's common. It's almost never the motor. You've got something hard caught between the blade and the deck, or the blade itself is hitting something.
First, safety: pull the battery out. Always.
Now, tip the mower on its side. Spin the blade by hand. If it grinds or catches, you've found the problem. Look for a rock, a dog toy, a thick stick, or a wire tie wrapped around the spindle.
Clear whatever's in there. While you're at it, check the blade. If it's nicked or bent from hitting something, it needs to be replaced. A wobbly blade makes a terrible noise.
If that didn't work: If the blade spins freely by hand but grinds when powered, then it's an internal issue with the motor or gearbox. That's a service call.
Heads up: Always do a quick walk of your lawn to pick up sticks and debris before you mow. It saves your blade and your ears.