i have a 00 civic si. it has DCsports header, aftermarket at, and straight pipe back to a muffler. for some odd reason i keep getting this rattle in the exhaust. i think that it is between the cat and the header. i have done everything i can think of to fix it. i out a exhaust donut on, then put a different one, then took them all of. nothing seems to work. and yes it is tightened down really well. was wondering if anyone else has had this problem. any help would be greatly appreciated. thanx