I find the 2004 Coupe I recently acquired to be much quieter than the 2005 Roadster I've had since new

Seriously though, it's incredible the amount of noise some tires can make. I had a set of BFGoodrich KDWs on another car and they were great when new, but when close to worn..... holy smokes the noise was so bad I thought I had a wheel bearing going out on me. Crazy thing was, braking to a stop light on smooth pavement from about 40mph the noise was crazy loud! New tires, noise gone.

On my 2005 Crossfire Roadster the original Continentals weren't terribly noisy, they just rode really harsh and didn't stick all that well. I mounted a set of Toyo Proxes T1R Sports and they're even quieter, ride better, and turn in is damn near instant. I freakin' love these tires.

On my 2004 Coupe, which I bought with totally shot tires, I recently installed a set of Sumitomos that I got on TireRack for just over $500/set in factory size. That car is actually very quiet inside now. I haven't taken any SPL readings but I could on the way home tonight (if I actually remember!).

By the way, these Sumitomos are a bit narrow and, had I thought about things when I bought them I would have opted for 275 cross section on the rear instead of the factory 255. I have 275s on the Roadster and they look great while the 255s look a bit stretched on the factory wheels of the Coupe.