This can be the sign of a failing display or a failing logic board. If you take a screen shot, then do those lines show up in the screen shot image? If YES, then it is a logic board issue. If NOT, then it is a display issue. There is also a cable that connects the display and the graphics output points on the Logic Board. This cable may be failing.
Try the following basic troubleshooting steps and see whether the issue gets resolved (If you have an Intel based Mac):
- Reset SMC by following the directions applicable to your MacBook here ➔ How to Reset SMC. If that does not solve things then-
- Reset NVRAM/PRAM by following the directions applicable to your MacBook here ➔ How to Reset NVRAM/PRAM. If that does not solve things then-
- Enter ➔ Safe Mode and see if the issue still exists in Safe mode. Log out of Safe Mode and then reboot computer. If that does not solve things then-
Finally if none of the above works, then you can have your MacBook Pro examined at the Apple Store or an Authorized Service Center or contact ➔ Apple Support
Axel F.