The sound is coming from the stand in the back where it connects to the base monitor. I just was adjusting the angle and I noticed it is not smooth, sounds like metal to metal.
Because the base is metal and the back of the monitor is metal, that's what the sound is. I think you've been in front of your computer a little too long...
Take a brisk walk outside, it's cold, but it's refreshing.
I have 2.. one of them makes no sound (smooth) and the other one makes a grinding noise. Not a big deal for me though... I don't adjust my monitor much. Even if I did ... I'm not sending this back or going to get a claim due to this issue.