i hope for your sake it is a exhaust rattle, My 97 had a "rattle" until i realized its a lifter inside the engine that has lost its tension and will rattle until oil comes into contact with it about 1 second after the engine has started. Sometimes its a very quiet tap tap tap tap tap and then sometimes its a loud TAP TAP TAP TAP TAP and it embarrasses me but im lucky to usually have no one around when I start my porsche which has just accured to me as very very very odd but true....
