catalytic converter

i think i am having problems with my catalytic converter. there is an awfull rattiling sound coming from underneath car. its like there is something loose in catalytic converter. has anyone ever had the same problem??? has anyone ever changed the converter?? how much am i looking at??? should i go ahead and put new mufflers and tips on also if i change converter. car has 125,000 miles on it 1998 aurora. i love car haven't had hardly any problems so far.

I have the same problem. It is intermittent, and seems to occur at low rpms. Floor it, and the sound goes away. I was quoted about $500 for a repair which I will have done.

I have 130,000 miles on my 97' Autobahn.

are you sure its not just the heat shield on the outside?