My right one has the same issue.
I have had 3 DIFFERENT units do the same exact thing ONLY on the right one so I believe there is a firmware issue.
This occurs both on iPhone (iOS 13.3.1) AND on Windows. It is not iOS-related
Timeline:
About a week and a half ago, I was watching a YouTube video when I started to notice a clicking/crackling noise from my Right AirPod. It would do this anytime my face moved, if I spoke, or if I gently tapped the AirPod, my ear, or the area around my ear. The Left AirPods was entirely unaffected. This clicking noise was so annoying that I had the Right AirPod swapped out. But, instead of this clicking sound (which was quite loud), I noticed a slight cracking sound and the Apple Rep told me ahead of time that they were well aware of this issue and many have complained of this and that swapping it out "may still result in the same issue" -- of course I still asked them to swap it...
I took those pairs home for a day but the crackling was annoying me so I brought them back the next day and requested that both the LEFT AND RIGHT be swapped in case there is some kind of issue with the left causing an issue with the right (unlikely but I have AppleCare+ and am entitled to as many replacements as necessary to have a bug-free product).
I got the THIRD pair back today and the Right AirPod STILL has a slight crackling noise when the above-mentioned actions occur. I have verified that they were all unique models by checking the S/Ns and this issue occurs ONLY in Right AirPods while on Noise Canceling or Transparency mode. It manifested itself the same way in both the "clicking"-type sound and the "crackling", "static" "echo"-like sound. I am going to make another master thread of this and also submit a bug report.