I doubt that the saddle rails/post clamp parts are carbon. perhaps the post shaft is. I'm not familiar with the post/rails clamp design on your bike, some are more likely to loosen or need high torque or lube. One way to start hunting down noises is to systematically taking one sub assembly apart, cleaning all and reassembling with proper lube/paste and tightness. Then ride and see if there's a change.

As is often mentioned on this forum noises can seen to come from one part but actually be from a different one. So also look at your bars/stem and the cranks/pedals. Andy