I don't know what it is but that is one thing I hate about the SHO is the way it sounds with or without an exhaust. Sounds kinda like a 4 banger with a fart can just a little deeper. I had a SW cat back and took it off and sold it, I just couldn't handle it. Not because it was too loud with my catless downpipes but just purely based on the tone. These cars sound like the old duratec engines just with more power.
So far I like the catless downpipes, they keep the same tone just a little louder. And I'm surprised at how little cat deletes amplify the sound, I was afraid going catless would be a lot louder but it wasn't.
Wish it sounded like my old G35 exhaust but I wish theG35's had turbos lol