I've been going through the exact same situation for some time. Just been clearing the code when it pops up. It's been off for a good while but I now have an annoying metallic vibration/rattle after cold start. I've heard the same noise on other cars I have owned and it is coming from inside the cat. Went to Ebay to get the best price I could find, $207 and change for an OEM Ford cat, $7 and change for an OEM Ford manifold gasket. Picked up the lower gasket from Vato Zone (Auto Zone here in Texas) for a few dollars. Will update after the job is done, probably this coming weekend.