It has been noted by numerous Infiniti G35 owners that they have experienced a squeaking of the rearview mirror.The following information is one way to resolve the issue.
First, you need a tube of Silicone. Clear caulk type recommended.
Next, with the mirror removed, find the center line on the underside of the mirror. However if you are worried about scratches, you can open it from the top.
Next, insert a small flat head screwdriver into the attaching center line, and mildly rotate until the two pieces separate to create a gap.
Then apply small amounts of silicone on the four posts in the back, and let dry. (You can also use a hair dryer to speed up the process) Apply silicone on the face where the plastic touches the glass.
Reassemble, and clean up any silicone residue on the glass with a paper towel.