hey...i just got my high flow cat installed on my 04 ralliart about 3 months ago on my header. i had no problem until now. i seem to get this loud rattling noise during start up and during idle. as i shift through my gears u can hear it rattling some more.... has anyone had this problem before or any clues? i checked underneath my car and nothing seemed broken. i dont kno if it could be an internal cat problem or just the heat shield surrounding it. any advice would help... thanks