You can try SLPONLINE.com I think they have some sound clips...
To tell you the truth I went to an SLP dealer who install these types of mufflers just to see what they sounded like...And let me tell you something I would have to be drunk to put them on. This guy had long-tube headers a short x pipe with an SLP Loud mouth Exhuast and it still sounded like total Crap...Sure its loud...But sounds like Garbage..It seems to be too Raspy for me, there isn't a deep tone to them, like what you would get with Flowmasters... SLP arn't really loud anyway, its only when you get on it and thats like over 3000 RPM.. They also gett annoyingly LOUD when there up that high in RPM..A word of advice...Don't get'em...Ssave your money...