2002 Z M6. SLP loudmouth and lid their is a rattle at 2500 rpms. Had the catback welded up but still rattle noise. Was under it today tightened up all the bolts to the clamps the guys that welded forgot to take off. Still rattling. Put my ear up to the exhaust pipe sould is comming out of the exhaust pipe. What the the hell could this be? Im thinking cats? 17.000 miles warranty should cover it? They going to bit*h about my LM?