In a new to me LJ I have been hearing this rattling noise at start up. It gets drowned by engine noise and music when driving but it is still slightly there when driving too. Some times it will go away though. The PO told me it was because "the cat is rattling against the transmission". Upon initial inspection it did look this way because the cat was resting on the corner of the transmission. Since my ownership I have installed a suspension and body lift so there is no longer contact with the cat and the transmission so obviously that isn't why it is rattling. I also just got a P0432 code "catalytic converter operating below minimum efficiency". I got out and put my ear to the third cat and it sounds like a coin is bouncing around in there. Where should I go from here?