Can you post a picture of the starter bendix while installed showing the relation of the bendix gear, starter shaft and the flywheel? Anyways, first you need to make sure the bendix unit is not stuck in the starter shaft. This can easily happen since after the engine starts, the pinion gear gets overrun by the flywheel due to high gear ratio, meaning instead of the pinion gear driving the flywheel, when engine starts, the flywheel will drive the pinion gear or bendix. As such, the bendix gear will screw back down to the starter shaft, and this can be a hard reset or not depending how long you held the switch in on position making the starter to continue turning and gaining speed (it is a series motor hence will continue to gain rpm if held for too long) and pushing back the bendix against the flywheel. But this time since the flywheel is already turning, it will not allow the pinion gear to engage thus you hear a metallic grinding noise.
So using a screwdriver, make sure the bendix gear is freely turning (and it should screw up to the starter shaft while you manually turn it) and riding up and down the shaft. While the gear is up, apply some light grease or oil where the bendix gear sits when idle. Then try again and let us know what happens. As I have mentioned apply some light bearing grease to the flywheel and pinion gear teeth. You can even do a simple test by spinning the bendix gear clockwise (looking form the top) hard like simulating a overrun and see if it gets stuck at the bottom of the shaft. If it does, you need to clear what causes it to get stuck for it is not supposed to be.
Note: Others vehemently object to greasing or oiling the starter shaft for the reason that it accumulates dirt or becoming a dirt magnet. This could be true but only if you decide to padlock the cowl and never to do any maintenance on the starter pinion after greasing it. The fact is, the starter pinion needs to be lubed every 30 days or more often especially if used in seawater.