It sounds like it's the Cats ( in that area) being loose or something..won't do it in park..but when i put in drive..it rattles until about 5 MPH and goes away. Getting louder. Vibration noise. It will do it when hot as well.

 

Sounds like Rusted out heat shields on the cats. They are spot welded to it. mine was like that till I ripped one off and safety wired the other one tight till it will rust out more so I can tear that one off too.

 

will look into it..thanks