Hello all. I have a cat converter rattle on my 2000 S40 (180K miles). Have an intermittent P0420 code as well on the CEL. Question. Can this rattle be fixed (tightented) or is the rattle coming from inside the preconverter itself and cannot be simply locked down? The rattle is coming from up forward of the metal mesh tube that connects to the downtube coming from the preconverter. As you know, the exhaust manifold connects to the preconverter, then a tube runs from there vertically down to the "bend" where the tube turns horizontal and meets the metal mesh tube, and then onto the main cat converter towards the rear of the car (underneath the rear seat area). So is this rattle a "flanging" problem that needs to be tightened, or what? Thanks in advance for your considered opinions and experience.

 

More then likely, it is coming from inside the cat but you would have to get under the car and shake it to know for sure.