my ego 56v mower is making a loud clicking or grinding noise from under the deck

Yeah, this one's common. It's almost always a foreign object caught in the blade or a damaged blade hub.

First, safety: Disconnect the battery. Tilt the mower on its side (with the air filter side up).

1. Visually check for a stick, rock, or wire wrapped around the blade (part number 1, 2, 26, or 27). Remove it.
2. Spin the blade by hand. If it grinds or clicks, inspect the blade bolt (part number 9) and the prevailing torque hexagon lock nut (part number 28). Ensure they're tight.
3. Look at the hubcap (part number 8, 36). If it's cracked or loose, it can cause misalignment and noise.

If that didn't work, the fan (part number 24) might be hitting the trail shield (part number 21) or the rear cover (part number 20). Check for bent components.

Heads up: Never check or work on the blade without removing the battery pack first.