Your starter motor isn’t disengaging when it’s supposed to, happened with mine too. Doesn’t mean anything bad on its own, but it will wear out faster and may be a sign that it’ll fail eventually. Mine did it for 2 years without kicking the bucket before I replaced it out of caution. Get the starter motor replaced or keep a spare in the car for when it fails, not super difficult to replace yourself as long as you have the tools with you.