Bill, I just moved up from a Torch Red 1998 C-5 Convertible to this pictured '06 C-6 convertible. I'm not sure about any insulation, but my C-5 was open from the cockpit into the trunk under top(when down), so I did get road noise and especially when the top was up. They sell a trunk to cockpit blocker for about $100 but after I saw it, I said heck I can make that myself and of course I never did.
On the C-6 the opening behind the seats is closed off and contains the rear speakers. It has a power top, so I'm not sure if that is to keep your hand out of there, but for sure any noise that is in the trunk, stays in the trunk. The car runs as quiet as an Impala (that is until I resently put some complementing exhaust on). Now just the hum of horse power, that responds when you say, "Giddy-Up'!!! God Bless, rick