did you installed oem camera or aftermarket?
If oem - there is some hardware problem.
You need NTSC camera not PAL, all video module have NTSC for rear camera input.
Turn key in pos 2, dont start engine and put in rear. You have to receive good picture.
aftermarket installation needs 2 relay. dont power camera from rear lights, it causes noise. install second relay to power camera directly from battery.
I had same problem,than installed second relay and problem solved.
Post result.