i have a 00 civic si that i have had for about 8 months. it is still a work in progress and funds are tight so its slow going. when i got the car the guy had some exhaust mods done. for some strange reason there was a rattle coming from the exhaust. i think it was between the header and catalytic converter(which was factory). i replaced the cat with a high flow and the rattle went away for awhile. recently it has returned with a vengeance. everything is tight and snug. i cant figure out what it is. anyone else have this problem and if so how to fix?