This was different from those of you that were having problems with the steering column. Mine was coming the the passenger side, and rattled pretty loud under moderate acceleration. It turned out to be the heat sheild on the exhaust manifold. The bolts were all tight. Not sure if it was hitting something from the back side or what, but I used a screwdriver to pry it away from the exhaust pipe (on the bottom of the sheild) a little bit, and put several dimples in the entire thing using a screwdriver and a hammer. I didn't beat the hell out of it, just small dimples to make it more rigid. The rattle is now completely gone. Hope this helps.

 

I just did the same thing about one hour ago. My tools of choice were a pry bar and screwdriver. I originally thought the noise was too deep and consistent to be a rattle but when I was laying under the truck looking up it became quite obvious. Also a big thanks to the people who posted the similar problems to give me a place to start.