I got a DVD of all this footage and reviews of about 10 exhausts for Libertys. They drive through tunnels and stuff, so its pretty kewl to get an idea of the sounds of different exhausts. I'm sure PhatGT has the same dvd too, you can go check it out.
I posted up a vid i did from a track day not long ago, somewhere in here. You'll notice the incar noise is very subtle, i'll see if i can load up something without any music etc, to give an idea.