my 04 focus svt exhaust rattles. It sounds like it is coming from the section that is somewhat flat after the exhaust comes off of the manifold where the O2 sensors plug in. When it is running, if I hit it with my hand it rattles more. Are there bevels inside that section that can come loose? or am I most likely hearing the rattling from the cat and it just sounds like it's in this section of the exhaust?