loud banging sound at ignition and then gets ok and runs smootly

What is your question?

My 2007 Toyota Corolla has been fine until the last two weeks. Every time I start the car, there is a loud banging sound. it sounds like something is trying to get out from underneath. it seems to be only on the passenger side centered in the middles. To my knowledge the car has not been hit as there is no damage that I can see. There are no leaks and no warning lights come on. I keep the car serviced. I looked underneath and see nothing dragging or sticking out. Any ideas? Thank you.