A ground loop is caused by the existence of more than one path to ground. If a signal is passed from one electronic component to another via an unbalanced connection, the difference in the ground potential causes an errant current to flow through the cables. This current flow can create a distortion in the video or audio signal. One type of ground loop interference, AC Beat, is exhibited as a bar of milky luminance that rolls from the bottom to the top of the screen. Ground loop is audible as a 60 Hz hum in the audio signal.
Can it be fixed?
If ground loop problems are recorded in the video or audio signal, they are only correctable through re-transfer of the content without the electrical anomalies in the system. Usually, this involves powering all devices in the video system using one source of electricity with all outlets serving power with minimal difference in ground potential.
Watch for the horizontal band rolling up caused by the ground loop.
An example of a ground loop problem that was recorded onto a 1/2” open reel tape