I can hear it without an AM radio! It's very clear but extremely quiet. My machine is muted and I'm trying to work out where in the world the audio is coming fr

I can hear it without an AM radio! It's very clear but extremely quiet. My machine is muted and I'm trying to work out where in the world the audio is coming from. I wonder if it's just the speakers in this monitor picking up the signal. Or one of my switched mode power supplies that also sometimes whines very quietly in the background.