I experienced a feeling I have never had before. (Past Simple + Present Perfect)
This sentence seems very strange and fishy to me, gramatically. Please confirm my doubts or tell me I'm wrong.
As you noticed,
I experienced a feeling I had never had before.
is more logical. If we change the second verb from "to have" to "to feel" it's clear to me that we must use past perfect and not present perfect.
I experienced a feeling I had never felt before.
It's more clear if we change the verb in the second clause from "to have" to another verb:
I saw a mountain I had never seen before.
(with a "have" there it sounds just ridiculous.) I think that, because the verb "to have" (to possess) is the same as the helping verb "to have" for the perfect, we sometimes get confused when forming a sentence where the verb is "had." That's why in the first sentence might be constructed with "have;" however, I think this is a speaker error (even 'descriptively') and that a native speaker would probably change it to "had" if they thought about it.