Squeaky Retina MacBook Pro upon pressure to bottom-right corner
This believe this is normal. I have experienced the same in my unibody non-retina MBP.

I carefully studied the back cover for wear marks. Then I took a close look at the logic board without touching it.


On the whole logic board you'll find tiny elastic sticks. They can be pushed a little. These sticks hold the aluminum bottom off the logic board.
I did not take any chances, therefore I applied insulating tape on every place of the aluminum bottom that the sticks can contact. Also I did not want to open the cover multiple times :)
Apply the tape again as it easily wears out.


Now the MBP does not make any of the previous mechanic noises anymore.





This is what the back cover looked like when I was done.