A little bit of background:
The factory 2001 exhaust was manufactured for FoMoCo by Arvin-Meritor. Many cobra owners have commented that the stock 2001 exhaust was somewhat on the "louder" side for factory exhaust systems. However, there is a consensus among many 99 and 01 owners that the post-fix 99 catback is the louder of the two stock systems.
Chances are the 01 that you listened to had an aftermarket system. Most owners have swapped out their factory Hpipe and catback by now, but there's still a chance that the 01 you heard was running a stock exhaust (unlikely).
That being said, if you are in search of an aftermarket exhaust system, read my reply in the following thread:
http://forums.stangnet.com/showthread.php?t=556678
Hope that helps.