rattling underneath 2011 silverado

I 2011 four door silverado, with a JL audio steath box under rear seat on the drivers side.  It is bolted down through the floor. I have all four doors dynamated and the installers put dynamat under the truck where the sub's are at, but there still is rattle from that area.  Under the truck it does not look like they dynamated all they way across where the sub is located. Could this be the problem or is there something else causing the rattling. 

Does the bass make it rattle?  Or is it a rattle while driving and hitting bumps issue?

Does it sound as if something is loose/banging? or the typical metal rattle. I never have an audio system, without undercoating the vehicle. Prevents rust, and eleminates rattles on almost every under car surface. As long as a car is made of metal, it will make some noise. Just simple physics.

Sounds like metal rattling together, but I do not see any loose metal.  I'm gonna try putting some more dynamat under the truck where the sub sit. It looks they just dynamated under the truck with what ever they left over from the doors and did cover enough area.  I know I did not tell them to put dynamat under the truck, so I'm sure that's what happened.  Thanks for input!