Weird..I noticed mine is creaking/squeaking too. Especially after reading this thread. The noise comes from the middle right back as well. That's basically around the area where the battery mounts to the MB. I assume the squeaking comes from the gap between the battery and the back case. I do feel a little bit of give if I squish it there a little compared to the other side. I suppose, since the battery is so big, just over a 1/4 the size of the kindle, it was difficult to put clips or supports on that portion of the case.
See video with good disection of the K3:
http://www.youtube.com/watch?v=lD-wPmowR-Y
I'm just going to put up with mine.