Try a Greddy Evo2. I have one with Helix UP/DP (completely catless) and it's only a bit louder than stock. I cannot even hear it on the highway (it's actully more audible at idle or low rpms than on the highway!)

 

Exhaust had a leak between DP - CBE and was incontact with the rear diff. The muffler shop installed 3in flanges on both and refitted the exhaust. It is quieter and less drone, but still more than I expected. I would have loved the COBB, but I've heard they are on back order forever and I thought they were comparable in sound levels from all the posative posts I read. That being said I heard a Blitz Nur Spec today and that was freakin loud. Still thinking of experimenting with the sprint car muffler.