What's wrong? First it could be the welds. All the name brand mufflers are robotically TIG welded, with imitation mufflers, you never know. Internal TIG welds must be done perfectly for sound quality or else rattling occurs. Second, you dont know the quality of the baffle. Name brand muffler companies like A'pex-i use high quality baffles. Third, you don't know the quality of the fiberglass wool that is back inside. Again, name brands use the highest quality packing. Fourth, name brands use stainless steel or titanium for the structure and for weight. You never know what imitation mufflers are made out of.