I think I know why my F355 sounds different than any of the others. when I took it to Tonkin, I told them whatever they did in the tune-up not to change anything in the timing or an ananomalous finding that would change the sound unless they absolutely had to. They came back to me and said they think they know why it sounds different. Apparently there is a little valve that bleeds hot exhaust into the Catalitic converters to preheat them. There is a little electric pump that drives the hot flow positively into the Cats. Apparently this valve is supposed to shut-off after two minutes when the Cats get warm. Well on my car this valve is stuck in the open position. Consistent with my disdain for political and ecological correctness - I directed them not to fix this valve - Tonkin in-effect assured me that it would have no effect on the way the car runs or the life of my exhaust system without coming out and saying it. I haven't seen a schematic of this goofy little system to satisfy my own technical curiosity but i have my fingers crossed it will still sound the same. It's just possible that this little system creates a resonance that otherwise isn't there.