I am having the same issue, I noticed it about a week ago under the screen directly above the power button. These are the best pictures I have at the moment.

If you enlarge the image the thin black band beneath the lower edge of the screen should be visible. Notice how the center above the power button is noticeably jagged.
I assume this is a manufacturing defect as I have not exposed the band to extreme temperatures or humidity, or done anything that should have caused this. Hopefully it will be covered under the manufacturers warranty...