I have a 5zigen Fireball Exhaust on my car and I'd say it's pretty quiet. It doesn't attract much attention from pigs if that's what you're looking for. At low rev's it has a nice low deep rumble but at high rev's it gets quieter. Good add on power too. If you really want to know how it sounds here's a video...
YouTube - rsx 5zigen fireball exhaust
It's got pretty good reviews for it too on carreview.com, it's rated 4.67 out of 5.