the interiors of our trucks are 15 plus year old sheetmetal... even from the factory they werent very quiet...after many miles of vibration they get noisy...
if you want quiet then you need to multi layer your approach
make sure all fasteners are tight... and there is no movement in body panels...
coating of the body in (like rattleguard) and out (like asphalt undercoating)gets rid of the tinny sounds...
to make it MORE quiet then you need sound deadener such as DYNAMAT inside your doors, on the firewall etc... then if you really want quiet you put in the factory sound deadener... including the engine compartment.. then carper or rubber floormat.... new window seals, chase down all the air sounds in your doors etc and stuff them with waterproof insulation etc... you could just keep going... but it will get quiet..
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