So a while back I replaced my second catalytic converters, the ones with the flexible pipes. It made a ton of noise before, and the flex pipes were shot. However, after that, the level of noise was still unacceptable. I thought maybe the installation was done wrong, or the mufflers need replacing, but neither of those were the case. It was driving me crazy.

Then the noise abated. I couldn't figure out why. I finally put two and two together. My right hand mirror shell was busted before I bought the truck. I temporarily fixed it with matte black duct tape. Turns out that's how the noise was getting into the cabin. I replaced the entire mirror last night, and the noise continued to be abated. Definitely a WTF moment.

 

Lol!!!!