I’d also be concerned about crunching noises.
I wouldn’t be satisfied with just a light scraping. I’d want it much cleaner. Maybe 10 seconds for each square foot with an angle grinder outfitted with a diamond cup wheel and you’d be down to bare plywood. Absent that, I’d use a rub brick (available at any box store in the masonry section). The rub brick is an abrasive block attached to a handle and is like sandpaper on steroids. It will grind through the old thinset mortar with a little elbow grease. It won’t be as clean as using that power tool, but it will smooth things out nicely.
