i just installed my stacks and have a few questions to the guys who have them, do u put a flex pipe? or just mount solid? got a vibration when in gear at a stop that im trying to get rid of. and looking for a muffler, but all i can do is a 9" round and no longer that a 23" body, with 4" in and out. any ideas? i love the look and its a head turner, i just want someting to take the edge off the exhaust note. i found one at napa which is 9" round and a 20" body for $75. 00. is it worth it?