Dash rattle

[Ben1029]

2020 gmc sierra SLT 5.3l 10speed

when driving at highway speed 65mph or higher it’s sound like marbles being shaken in a glass jar. We removed A pillar trim on passenger side, upper and lower glove box, cabin air filter, passenger speaker and cover, passenger fuse panel cover, center vent cover by window and removed radio antenna. We tightened down cab mounting bolts to spec, tightened running boards, tightened wiper mounting transmission assembly, replaced 3 plastic tree clips and taped them, tightened blower housing bolts and tightened passenger Side mirror and noise is still their. Need some assistance to help find noise because I’m not paying $209hr for someone to look at my truck.

Thanks 

[sswails]

Probably the rear seat. There is a metal piece that rattles when the seats are in the down position. It’s part of the hinge. Both outboard seats have it. Sort of looks like this. Mine is silver though. I had to put some foam tape where it rattles. 

Edited January 24 by sswails

[Ben1029]

No luck, we removed rear seats and still rattles on front A-pillar area