[Beav]

The apparent question is which end of the cat was the mesh in? At the 'in' or the 'out'? If it was at the 'in' the substrate sometimes breaks loose and rolls around until it forms a ball which can eventually travel further downstream. These balls can intermittently plug up a pipe, resonator or muffler. Best check is to drop the entire exhaust and tip it up and down and listen for something rolling around inside. Sometimes you can retrieve the culprit, other times you just have to replace the part it's trapped in.