Ok I installed my h-pipe and one of teh bolts was loose that connects to the flow tube so i tighten that up so the muffler is no longer hitting the underbody. But I still have this vibration at low RPM's like 4-500 when I'm stopped and the brake is applied. If I brake tork it a little bit up to like 700 rpm's its fine but down low its vibrates like crazy. What the hell could this be? Do you guys think that somewhere the pipe is touching the body causing it to vibrate or is it in the motor because of the cats being gone? What do you guys idle at when stopped at a Stoplight?