U2412M has tiny black line on screen

Hi,

I bought a U2412M from amazon last week. After setting it up, I found a tiny black line on screen. Then I removed all the connection between my Mac and ran the diagnose mode on my monitor. The black line only shows when the screen turns grey. It is fine when it turns into red blue black and white.

Please see the pictures below. 

http://goo.gl/HW0fud

http://goo.gl/DWkBg2

http://goo.gl/3saEzX

Thanks