Hi @riberto
Try moving the screen slowly back and forth to see if you can make the problem happen or if it is happening to make it stop happening.
If nothing happens then try connecting an external monitor (TV?) to the laptop's HDMI port and check what the laptop's display is when seen on it. Don't forget to press the Fn + F8 keys (both together) to toggle the display output from the laptop screen to the external monitor to both screens on together.
If the external monitor display is OK it may be a problem with the video cable between the motherboard and the LCD panel, the video cable connection at either end, motherboard or panel or the panel itself.
Here's the [https://dl.dell.com/topicspdf/precision-15-5530-laptop_owners-manual_en-us.pdf|service manual] for the laptop. Go to p.37 to view the procedure to remove the display assembly. This will allow you to check the video cable connection on the motherboard and if it appears to be OK you will have to further disassemble to check the panel cable connection or to change the LCD panel.