Hi, Im smelling unburned gas in the cabin, could that be a symptom of a failing cat also?

Thanx

 

I getting a P0138 code from my car. I thought maybe my 02 sensor has gone bad, but could it be my Cat is bad.

I sometimes hear a slight clunk noise from under the rear seats. It's most likely to happen when coming to a stop.

 

The cat would be located more under or forward of the front passenger seat. The area under the rear passenger seats is fuel tank.

 

Thanks, Alnielsen. Big help.