Macbook pro (Retina 15 inch Late 2013) Horizontal gray line across screen I have bought this computer New at the Apple Store in 2014.

Since yesterday it's showing horizontal gray lines across the screen. I suspect a hardware defect because that's how my 2 others macs older started showing problems too.

All updates are installed and restarted the computer a few times. 

Anyone would know if this is really an hardware issue? If it is probably looks at very expensive repair.
This is definitely a hardware defect, because, as Tetsujin mentioned, the lines do not show up on the picture. I would suggest going to an Apple retail store or otherwise the store you bought the Macbook to get it checked up. Are you still under warranty/AppleCare?