It's louder in the car for sure but not quite as loud outside the car .
Here are a couple videos of my old Cobra with the Magnaflow catback and UPR x-pipe . The first video is with pipes out the back and the second is with them dumped .
http://www.carolinahorsepower.com/Jeff/812run.wmv
http://www.carolinahorsepower.com/Jeff/Jeff2.wmv