I represent ASA Electronics, the producer of the JENSEN brand of televisions, stereos, and speakers, the Voyager brand of observation monitors and cameras, and the Advent brand of appliances. At ASA, we strive to provide excellent customer service and product satisfaction and would like to offer some assistance.
What you are describing most likely is a connection issue between the rear camera and the monitor or it is a failing rear camera. You don't mention the models, however, it sounds like you have our AOM7694 Quad-view monitor. If your rear camera is a standard non-tilting camera, you can try swapping the camera inputs of the rear camera with one of the side cameras at the monitor's input harness. If the symptom continues on the rear camera while connected to input 2 or 3, this should rule out the monitor.
Next, verify the camera & camera cable are securely connected at the rear of the coach. If so, bring the rear camera inside the coach and plug direct to the monitor (bypassing the main camera cable). If the symptom goes away, most likely there is a cable problem. If the symptom persists, most likely the camera is failing.
If the trouble persists or you have any questions, please feel free to call our Technical Services department for further assistance at 877-845-8750 M-F 8:00AM to 6:00PM EDT.
ASA Electronics - JENSEN, Voyager, iN-Command & Advent Tech Support Team