I did get quotes from a couple of car audio shops, which ranged about $400-$450. The cost of the amount dynamat material needed is about $150 (with a total added weight of about 30-40lbs). I also found came across a webpage where someone had installed soundproofing in the doors of a ’13 or ’14 pathfinder, which seems very similar (if not nearly identical in structure/framing to the QX60). With that said, I will first see if I can remove the door paneling myself. If successful with no real issues, then I foresee adding the sound dampening material to a few spots on the inside of the outer door sheet metal, around the speaker housing of the inner door frame, and in a few other spots of the inner door frame. That’s the plan, but we’ll see how it goes (e.g., time, other competing priorities, ease/level of effort).
A consideration I currently have is whether or not the sound dampening sheets will make a significant difference in the QX60. I’m sure it makes a huge difference in other vehicles like a Civic or Chrysler 200 where the interior is a bit noisier than a luxury vehicle, but am not sure about the QX60 since it’s a luxury vehicle that is fairly quiet enough and should already have some sound dampening material in the doors. Also, while I’m sure the sound dampening will help some (if not significantly), there’s still some noise and vibrations on the floor board side (as well as windows). I don’t plan to add sound dampening sheets on the floorboard mainly because it seems a bit difficult considering all the carpeting and Styrofoam underneath it. Plus the car audio shops recommended against it for the QX60. With that said, I am considering spraying rubberized undercoating in addition to some that already exist underneath the vehicle (which I noticed when getting underneath the car to install my new running boards) as well as to the wheel well linings.