Every since C5 when the torsional rigidity was 4.5 times stronger compared to the outgoing C4 with the Hydroformed side frame rails, most of the squeaks and rattles in the Corvettes disappeared.
Not knowing your car, options, what happens when you take the speed curbs or the curbs your describing straight on if you get any creaking then,
can you remove some of the trim pieces behind the door that cover the seatbelt and run the some route?
I've had three C8's and there is no creaking going over speed bumps, on choppy surfaces or running on the racetrack.
That also applies to the roof in or out. It's always a challenge to find these issues but you can start your process of elimination to figure it out.