Do you mean that the display is shimmering? If so, this is a problem that seems to affect some 7" panels. People who report it say it goes away if they touch the ribbon cable connector on the back of the panel.
The 4.3 and 5" panels have some sort of shielding over the ribbon cable, but the 7" panels don't. Maybe they need it. If I ever get a panel with this problem, that's what I will try.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
