In an analog signal it is alternating currents that mimic the sound wave; so in my mind DC should never produce audio but is that true? In a ground loop the noise is caused by differences in ground potential of either side of the loop allowing current to flow but is it AC or DC?
Is a ground loop caused by voltage potential between the grounds only or that plus EMI combined?
To add to the question clearificarion. If I have an unbalanced output from a mixer to an input with a different ground I will get noise on the receiving input even when no signal is being sent from the mixing desk. What is making the current alternate between ground references? This was the case recently with a church that asked me to fix a buzzing in their video feeds. Fixed it with an 8 dollar transformer from amazon because they did not want to convert to balanced equipment and proper interfaces but this is beside the point of my question. I’m just trying to actually understand physically how it works rather than just knowing how to prevent it