I'm not a rocket scientist or a physicist, but aren't both those examples a form of energy loss? The CF "absorbing" energy and the steel transforming the energy into sympathetic vibrations that eminate as noise? I think the difference would be that the energy that the CF loses happens very rapidly and the energy that the steel loss happens slowly.

For practical purposes though, I suggest a counterexample. I used to own a Vitus 979, which at the age of 18 was my "dream bike." I quickly discovered that I hated it. On every down stroke of the pedals, the entire BB, seat tube, down tube and chainstay interface would rock back and forth so that my chainrings would always rub on the front derailleur. In fact, if I really pushed hard (back when I used to have knees) I could actually get the front to shift off the large chainring.

I discovered that stiffness is important in bicycles, and yes there are differences among frames and tubing materials.