I have a new Herman Miller Mirra chair. I love it and do not want to return it, but it makes irritatingly loud creaking noises when I shift my weight or recline.
The source of the noise is the loose plastic shell that covers the recline assembly and is gently secured with S-clips. Any force against this hollow shell makes it deform slightly and produces the sound. Attempting to damp the noise by padding the loose areas of the shell to resist deforming does not help.