That sounds like the ratcheting sound made by the belt slipping a tooth. With a 1-1/2" deflection it is entirely possible to do this. That is on the looser side. If it happens again, either tighten the belt or don't jump on it so hard. I would tend to keep the belt on the loose side as it is better for the bevel box, bearings and seals as well as the sprocket.
So the choice is: "Doc, it hurts when I do this!" "Then don't do that!"
or
Tighten it up and hope that doesn't cause other problems.
