Seems to me that alot of exhaust drone would come from underneath not from the side (doors). If you want to quiet a vehicle it needs high density foam or insulation on the underside/rear of the cab and not so much the doors. Just my .02...

 

The doors is more wind noise and all that more than anything ( 70mph on a populated highway ), which is very minimal on every day driving. It is the jambs and closers of the door that need better sealed for overall noise however I don't know if that is highly achievable.

 

If by foam insulation like the stuff dynamite sells as the "hoodliner" is what your referring to that does nothing for drone also. Gone done passing that road. Don't recommend it. Now that is wasted money :-(

 

Yeah as I mentioned before, I've done the whole Dynamat thing in days past. Floors, back wall, doors, ect, ect. It is expensive and alot of work to remove the interior.
It does very little to eliminate drone.
Thats why it was cheaper for me to simply go back to a stock exhaust to quieten my interior comfort. Guy's I'm not kidding when I say I feel no loss of power whatsoever going back to stock exhaust. It actually feels stronger now with much more "usable" low rpm torque.

I feel that if you were to use small mufflers near the end of the tailpipes like used on the new late Mustang GT's instead of under the cab there would be no drone, and it would still sound great.

(Maybe?)

 

they don't have to be, my green truck is very neighbor / family friendly yet still has a slight rumble thru the exhaust