i got my muffler installed about a month ago and now the thing shakes and vibrates as soon as i start the engine. people say it could be the welding and some are saying its the bushings? im not sure because i dont know much about this kind of problem. it also spits out black dirt. this problem jus recently came up. as soon as the engine starts up. black dirt jus spits out along with smoke. A LOT of smoke. help me out.