One of the main contributors to noise in the cabin is an exhaust drone that you hear at between about 1800 and 2500 RPMs.
In my opinion, on my car - this is the predominant noise source. You can read about it here…
https://pantera.infopop.cc/top...060#2586368011486060
Anecdotally, I have heard….
1. Some people have fixed it (eliminated the drone) by cutting baffles out of their ANSA mufflers. This requires that you cut open the muffler cans, remove parts, and install angle iron flow diverters, and then weld them back up.
2. Some aftermarket mufflers say that they don’t have it the sound, but I can’t tell you which ones do, or don’t.
3. Some people say that the sound is channeled up to the roof or the drivers ears to the roof through the air space in the metal pillars behind the drivers / passenger window (the cavity acts as a waveguide) and that putting insulation in these channels can help to reduce the sound transmission.
(I have not verified any of these by experiment.)
Rocky
PS. Muffler mods can be accomplished after you get the car driving, so you don’t try to fix a problem that you may or may not have….