What is an APR "quiet" or "loud" catback (from ECS Tuning website)??
 

<ul><li><a href="http://www.ecstuning.com/00s4exhaust2nd.htm">http://www.ecstuning.com/00s4exhaust2nd.htm</a</li></ul>

"loud" is probably their first-generation exhaust....
 

...with the single muffler (or is it a resonator?). I guess a lot of people thought it was too loud, so APR designed a new system with 2 mufflers (I guess one is technically a resonator) and it's much quieter.

See Mark's post below with some more info.<ul><li><a href="https://forums.audiworld.com/s4/msgs/423664.phtml">https://forums.audiworld.com/s4/msgs/423664.phtml</a></li></ul>

Thanks Andy