Tap cat. converter with a rubber hammer to see if it is the problem. If not then try other cmponets where it sounds like it is comming from! May need it on a lift to help find the noise. Possible engine timing componet, let a mechanic listen to it if possible.
What kinda information? Its a ford expedition 2007 when i start it up not ever time but manly when its siting for about two hours or longer it makes like a rattle nosies but only when it starts not all the not when i drive or any other time.