I'm not sure if anyone has resolved or repeated the problems that Notout86 was having.
It sounds to me like the signal is degraded coming from the camera. My guess is that it is probably due to noise induced by the fact that the shielded wire going to the cameras must exit the shield to go to the PCB board.
It could be noise resulting from the other camera or it could be other electrical noise from something else in the car.
Things to try:
-Step up the voltage to the noisy camera. Normally, higher voltage will improve camera signal strength as long as it is within the rating of the camera.(you can use a relay harness like this to provide 12V vs. 6V:
http://www.autoharnesshouse.com/19867.html)
-Double/Triple check anything that you think is grounded(check it to a chassis ground point elsewhere on the car...like a door hinge)
-Try to maintain the video wires inside the shielded cable for as much of the wire run as possible(Run the wire straight to the relay)
-Turn off the unused camera(one less thing to create signal noise). This can be done by adding another relay. Here is an update the the diagram that I previously drew:
Edit: Hey....another thought: Are you seeing the noise on both cameras or only on one of them?