It’s often very hard to isolate the problem. Easiest way to find out is to swap the seat post; if the noise disappears, then you’ve found your problem.
Buy a used alloy seat post from Phoenix Bikes. It’ll only cost a couple of bucks. Make sure you get the right size, though.
(Just a guess on the sound: since it’s a carbon wrap post, maybe the carbon weave and alloy are expanding at different rates?)
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