I have a 2001 reg.cab. with 50k miles. I have fought a rattle in my dash to a point I considered selling the truck, to someone not as discerning as I am. It was in the drivers side dash, almost directly behind the a/c outlet. It sounded like heavy plastic, like maybe a/c duct, banging together. I finally took it to my local mechanic. He just diagnosed and fixed it. It was the slip joint in the steering shaft. He had to replace the steering shaft. AAAHHHH silence!!!