Sound Insulation

[Chad-1stGen]

I honestly doubt you will see any difference in decibel level from the exhaust with the addition of sound deadener. And definitely no difference in rear gear whine. Sound deadener reduces the panel harmonics / vibrations where it is placed. Generally, those aren't caused much by exhaust or ring gear whine.

I didn't notice much difference in either of those when I pulled a bunch of sound deadening and foam insulation out of my 68 Camaro. The interior got a tiny bit louder from road noise. But IMO the loud exhaust drowned out most of the benefit of the sound deadening I had previously added. That and the increased wind noise these cars tend to have over modern cars.