Answer
It looks to be a "ground loop interference".
An earth loop interference may occur when there is more that one ground or earth between two pieces of
equipment. Because there is multiple ground paths, loops are formed in which current can flow. The current flows
through the shield of coaxial cable and it picks the interference up and carries it to the inputs of CCTV equipment.
This equipment interprets this interference as part of the video signal and displays it on the monitor as a rolling
“hum bar”.
I suggest to use our Ground Loop Isolator (PN: 1101600) This item terminates ground loop currents in a cable and blocks the hum and interference carried in the ground loop. It should resolve the problem.

Answer

Every time you convert a signal or pass through a connector, there will be some signal loss. A point-to-point connection with great quality UTP cable is the best installation. Certain environments and applications will degrade twisted pair transmission performance. For example:
- balun performance may be compromised in facilities with excessive RF interference, such as factories with large AC motors.
- twisted pair cabling carrying an audio-visual signal should not be run within one foot (30cms) of fluorescent lights.
- cable carrying an audio-visual signal should not be run for more than three feet (92 cms) parallel to high voltage lines. Ideally, twisted pair cables which must cross high voltage lines should do so at a 90 degree angle.
- twisted pair cabling carrying an audio-visual signal should not be passively split or routed through an ethernet hub or switcher. Cat 5 carrying an audio-visual signal may be run through a passive patch bay as long as point-to-point connectivity is maintained.
- data, such as computer ethernet traffic, should not run on the same twisted pair cable as your audio-visual signal.
- balun performance may be compromised with excessive jumping and signal conversions.
Try to maintain a point-to-point connection, or if impossible, use an active product (PN: 121TR1)