In Park and Neutral, the truck is great, however at low speeds and switching into Reverse and Drive, the truck makes a loud rattling sound underneath the truck. Ive had this problem before, it was just an exhaust bracket. I can't find the noise and it seems to be coming from deeper and I can't reach in there. What should i do?

 

Sounds like a heat shield weld broke. Follow the exhaust system and check all of the heat shields. There are also some by the glow plugs that can get bent or crack and vibrate/rattle.

 

Hopefully its nothing that I can't reach. Thanks!