I have a loud metal clanging sound that seems to be coming from my catalytic converter. It sounds like someone is dropping a quarter on it is the best way I can describe it. It occurs once every 20 seconds when cold start then occurs more frequent when warm. I was thinking that it was the exhaust just expanding and contracting but when I started it cold the other day within 30 seconds it was clanging so I am assuming it is not expansion. I am takng the car in for an oil change so I will have them look at it just curious as to what it may be so that the dealership can't play any games. The car is stock 19000 miles. Thanks

-Brian

Good chance you broke off a chunk of the brick of material in your Cat. If that's the case, there's no way to fix it other than getting the dealership to buy you a new cat. It's easy to check though. Just let them pull the exhaust off and rattle it around; a piece should fall out.