Originally Posted by FriendlyFire
I haven't really looked myself, but if those cats have 02 sensors in or after them, their removal may cause fault codes.
I just swapped a Flowmaster 40 in place of the stock muffler until I can afford a full true dual system. The 40 did make it louder, but has a terrible drone from 2000-2800rpm. Above that, it sounds great. (eh, it was $60.)
I have listened to every exhaust video I could find out there, and there is one XF rallycrossing on Youtube; The guy has the stock cats, but true dual with Flowmaster Delta 10's and it is the best I have heard yet (it's all personal taste, though!) :
YouTube - ‪Custom Crossfire Exhaust‬‏
I went with a flowmaster and it sounded great but WAY to loud inside the car AND the drone was pretty bad too.
The rear cats can be removed w/out any o2 sensor problems causae the sensors are in the front cats. Id be sure to check with your inspection station to see if they will pass it w/out them. Im wanting to dothis mod but am getting mixed signals from different inspectors.