Originally Posted by Zaggeron

2010 Nissan 370Z Test Drive on Edmunds.com

"With the top down and the windows up, the 2010 Nissan 370Z Roadster's cockpit is virtually free of wind buffeting, allowing those within to converse without having to shout. And as we mentioned earlier, with the cockpit closed up, the roadster is quieter on the freeway than the coupe. We asked Nissan about it, and the carmaker attributed it to the fact that the convertible has a partition between the passenger and cargo areas, whereas the coupe has an open area that ostensibly admits more noise toward the cockpit."

Looks like a fairly subjective observation ... they didn't apples to apples compare the coupe to the roadster with a db meter along the same roadway. It's a fairly believable explanation though. I've got fairly decent roads around where I live and I don't notice much road noise with the top up. I imagine that the roadster might be noisier on rougher roads given it's not quite as still as the coupe