ive been worrying about having a loud exhuast too, just found this on phase2 looks pretty decent and ill probally go with this after i get my swap done. its supposed to be really quiet.
http://www.phase2motortrend.com/rsrexcat19ni.html
theres something else that caught my eye ......adjustable exhaust valve or something. o well check it out
http://www.phase2motortrend.com/jstyladconva.html