Second Skin Audio, Dynamat, HushMat, or Vibro Solutions all make dampening material specific for vehicles.
A combination of materials is the ticket (vibration dampening, heat/sound barrier & noise isolation). This is what current high end cars utilize in addition to coatings & specialty glass.
My Square-body crew-cab dually has a big block, 1 3/4" full length headers, & 3" exhaust (3" in/out mufflers under the back seat floor pan) w/a 'H' pipe. The exhaust tubing reduces down to 2.5" after the mufflers & dumps @ the rear bumper It has enough umph to trigger car alarms when pulling through an apartment complex. Zero drone & very quiet inside. I used the Second Skin product line (vibration/temp dampening pad/s, closed cell foam sound barrier, MLV sheet isolation). I had never used the stuff before but wanted the interior of my truck quiet w/the windows up. I got what I wanted.
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