honda hrn216 making a horrible vibration and loud noise, blade hit a rock. what do i check?

You have a bent or damaged blade and likely a damaged blade holder. Striking objects causes severe engine damage not covered by warranty.

Immediate actions:

1. Turn fuel valve OFF. Disconnect spark plug cap.
2. Tilt mower right side up (fuel cap up).
3. Inspect both blades for bends, cracks, or damage. Inspect the blade holder and mounting surface.

If the blade is bent or the holder is damaged, take the mower to an authorized Honda dealer for inspection and replacement. Do not operate the mower.

Heads up: Always install both blades as a set. A dull blade can be sharpened, but a bent or cracked blade must be replaced.