[JFP in PA]

You do not need to take the starter apart, but you do need to remove it from the car.

The Bendix drive on the nose of the starter is either dirty or corroded, or both; and is sticking partially engaged with the flywheel, causing the noise. The Bendix assembly needs to be cleaned and they lubricated with DuPont spray dry Teflon lubricant, which will not attract dirt but will keep the assembly moving freely. You can find the lubricant at most home centers like Lowes.