That day I noticed my rattle in the replacement L APP, I reached out to Apple Support on-line. They escalated the case right away and attempted to do another express replacement on that single ear. There was a problem (since my initial replacement, AC+ expired) so I was forced to go into my local store. An appointment was created for the next day. I went there, just to find out they didn't have any L's so they had to order it. A few days later it came in, and I went back and swapped it.
I can confirm that this replacement does not have the problem. So at least for now, my R and L replacements are good.
I can confirm that this replacement does not have the problem. So at least for now, my R and L replacements are good.