I'm with kungfudevil on this one, Pontiacs (as well as 99.9999% of all American cars) are complete garbage, from the cheap plastic interiors to the poorly-engineered drivetrains to the ugliest designs in the entire automotive world. I kept expecting someone to say the thread was a joke.
I don't know what you guys are talking about when it comes to road noise. I've got the plexiglass rear screen, so maybe that's why I don't have any noise, but I'll tell you - my car is very quiet (almost silent) at freeway speed. So quiet that my girlfriend and I can carry on a complete conversation at normal volume. I also do not get any wind turbulence in the cabin to speak of, unless I have the windows down.
If anybody would like, I have a professional field recorder (my girlfriend sings opera) with a very nice unidirectional shure mic, and can drive around with the top down and record how loud it is, and post the MP3 here. If your car is louder than mine, you might want to look into the plexiglass screen, or maybe have your local MB dealer check it out.
Also, I don't have body flex issues. I've driven my SLK-350 at about 135-140mph across a mountain pass, with the top down, and it felt completely solid. At one point, I was taking 30-40 deg turns at well over 90mph with no probs at all, and I really don't get any creaks/squeaks from the body when hitting bumps, etc.
I think if you're hearing a ton of noise, it might be time to check into a new set of tires. If you're hearing a lot of body noise when cornering or hitting bumps, you might want to have your springs and shocks checked and perhaps replace them. You shouldn't be hearing that stuff. My SLK is a 2005 model with about 28k miles, and I have none of the symptoms described here.
I previously owned a Lexus LS430, and the SLK is just as quiet with the top up. With the top down, it only really gets loud when I'm hammering on it, and that kinda noise is pure bliss to my ears.