18 months ago I had the exhaust system under the car replaced for about $1000, because it was making a loud noise and the check engine light was on. The mechanic said that it cost so much because the exhaust "pipe" had a catalytic converter in it. Now my check engine light is on and the mechanic (after replacing the O2 sensor) says that it needs a new catalytic converter for about $600 and that this a "different" catalytic converter and not covered under his 50,000 mile warranty from his first installation. Are there TWO Catalytic converters or am I getting ripped off?? Thanks, John B.