I am looking to buy a 2005 3500 6.6 engine. The truck was clean inside and out but I noticed whenever I let off the gas then pushed it again it made a popping noise that sounded like it came from the mid area of the truck. Any ideas on what this popping noise could be. I only hear it when I let off the gas then push the gas again. Thanks for your help

 

You might start by checking the entire exhaust system over.