Well, my wifes Accord finally turned 110,000 miles. So far so good with this car. We have our first engine fault code come up.PO420. I did a search here and it seems like its the Catalytic Converter but could be an o2 sensor. From the diagram I found online it looks like there's two catalytic converters.We been hearinga noise hear and there and sounds like a pice of metal bouncing around inside the muffler. So i definately think it's the catalytic converter. How do I know which one is bad?Oh...and this is a 4cyl EX.