I have the American Thunder Flowmaster cat-back on my GT. I love how it sounds. Not too loud, but loud enough
http://www.youtube.com/watch?v=b0H7PLDz9t0 (ignore the music)
http://www.youtube.com/watch?v=qa07UTh0ZHc
http://www.youtube.com/watch?v=b0H7PLDz9t0 (ignore the music)
http://www.youtube.com/watch?v=qa07UTh0ZHc