Arrhh! Another problem! Engine check light on!

[Xotik H3]

It does, but in my experience a Cat will clog, and choke exhaust flow through it. Not sure what would rattle... not saying it would not, just don't know what would case it to rattle. If you do a search for a cross view of the inside, there are no part to come loose on later cats, after the late 90's.