I think it might be more accurate to say that breaking a ground loop prevents a connection between the audio/video or network grounding- one of the definitions from when I was working in 12V audio was "A ground loop occurs when the ground from an audio circuit or power supply impinges on the other.

The problems we generally see are on the cable feed when the installers don't do their job correctly, part of the system is using one phase of the electrical service feed and something else is using the other phase or if the wiring has resistance on the neutral and/or ground. This applies mostly to power supply using DC, but it can cause problems for us, too. OTOH, I have eliminated ground loops/noise in 12V and AV systems of the type we commonly work with by connecting a cable shield to the chassis of a piece of equipment.

Breaking the connection on the two conductors in an unbalanced audio/video feed often solves the problem but a lot depends on how this is done.

Good point about the balun picking coupling with power cords or possibly, power transformers.