what does a loose cat or per cat sound like when it is loose . i got a sound like a beer bottle rattling around at low rpm's and its not the heat sheilds 
it is a small Catalytic Converter that is befor the big main cat its close to the manafold and block . i am sure you truck has a few of them if you have a 2004What is a "per cat"?
it is a small Catalytic Converter that is befor the big main cat its close to the manafold and block . i am sure you truck has a few of them if you have a 2004