Monitor causes humming in speakers

I’ve recently encountered a strange issue with a computer who’s speakers constantly emit a loud humming noise. I’ve tried swapping out sound cards and speakers with no success. I also tried moving the speakers & cables to the floor to eliminate cross-talk from power or other cables – no soup. By chance, I happened to turn off the monitor and the sound stopped. Also, any time I change a monitor settings (resolution, refresh, etc.) the sound changes in pitch.

As I’ve never encountered this before I’m hoping someone can help. My next moves are to install a new video card and/or monitor to see if that resolves the issue.

Thanks,
Ash