well my mac has been serviced twice by apple. One time the engineer said its normal the second time at a different AASP the engineers found it not normal so they sent a video to apple both said the noises is from the spring locks on the logic board, they cannot do anything nor replace the logic board unless I have performance issues. I had a polite talk and told them after plonking a huge deal of cash on a top of line macbook i do not feel great to have a clicking noise, they told me that they tried their best but they cannot do anything unless apple authorizes them to do so. I gave up on it, we have no apple stores here so things are slightly complicated, maybe you may have luck at a genius bar.