My 09 F150 has a buzzing rattle sound around 2000 rpms not sure what it could be. The truck makes the sound in sound in park or in gear and generally goes away when warm. Ive included a you tube video of noise which sounds like it coming from underneath the truck.

https://www.youtube.com/watch?v=kMDKbmB3xLc

 

Check your exhaust heat shields.

 

Yup, I had a catylitic converter shield that buzzed worse than Snoop Diggity Dog.

 

I have the same issue. Is the exhaust heat shield something you can fix on your own? ie tighten a bolt or two?