The biggest concern with my 2007 G35 is the road noise when driving on Interstate highway. Some roads are much quieter than others but more often 70mph on the interstate creates fatiguing noise. I turn the music off because it just creates more fatigue.
The road can make around a 10db difference and quite roads are in the minority. I avoid driving the car on 3+ hour road trips due to this issue.

I have seen comments about tires and sound deadening.

My tires are Potenza RE970AS Pole Position

I am interested in what you have done to quiet the noise. SPL levels would be of interest. Interstate highways are my interest. 30-40 mph residential roads are less an issue (not great though).

 

I have a moving blanket that's cut to fit under my rear seat cushion over the fuel tank access, it tucks into the carpet below the rear seat and extends all the way to the trunk. It's crazy how much noise comes up through the rear seat area particularly from the rear differential whining at speed (that annoying humming sound coming from the rear of the coupes).

That was the only part that really annoyed me, the blanket fixed it. The factory sound deadening pad isn't cut very well and there's a lot of exposed metal around the edges, basically I used it as a template for cutting the blanket, made everything about 6 inches bigger on each side, then trimmed the moving blanket up a little near the edges that wouldn't tuck in nicely.

I think I folded the moving blanket up 3x, to hold the layers together it's just a bunch of safety pins around the edge every 18 inches or so.

 

Check the audio sub-forum for threads. There's information in there about how folks use Dynamat (expensive) and similar products (less expensive but perhaps not quite as effective...folks debate it). It'll tell you where they put it and how much of it (interestingly, it's not used to blanket entire areas; all it takes is smaller squares strategically placed. But it's a lot of removing interior panels, etc., etc., etc....

 

Doesn't Dynamat make the car heavier ?

I once removed the rear seat and drove the car for a few weeks. It was super noisy, so I have heard the rear seat area being definitely a noise source with the fuel pump.

 

It's not that heavy unless you're trying to cover the entire floorpan. Selectively adding to just the noisy parts of the car you will probably add 10 lbs tops, covering an entire floorpan + firewall + trunk you'll probably use 25-30 lbs.

 

About right...120 sqft x (0.30-0.45) lbs.
Selected squares at centers of each floor pan, trunk,firewall and door skins might do it.