Car was making loud rattling knocking noise. Call dealership and describe the complaint and told them a mechanic said the problem was the catalytic converter. I was told its not covered under warranty. Would cost approximately 800.00 to fix. Call extended warranty company. They stated its part of the exhaust system not covered under extended warranty. Took to a mechanic he did not completely fix the problem but altered it to stop the noise. But when it's cold a whole lot of smoke comes out of the exhaust pipe.