If you want something different from a GReddy of Apex'i which everyone has, you can go for a 5Zigen Fireball rear system. They are not loud at all and have a nice deep sound when accelerating. At idle, it sounds stock so you dont attract unwanted attention from the cops. Heres what a v6 version looks like. 4-cylinder looks the same, just only with 1 instead of 2.