06 buick 3800 engine knock

I have a 06 lacrosse w/ 3800 engine less than 50k. Has anyone experienced this scenario? Only when first started in the morning, a Knocking, which is loud enough I can distinctly hear it 60 to 80 feet away, sounds loudest underneath the engine. Gradually goes away as it runs and almost completely in 5 mins. completely gone in 10 mins. and won’t do it the rest of the day till the next day. thanks, Dwayne