https://vocaroo.com/115rI7pHM1XK
listen to that. What can cause this noise?
the noise is not constant. it comes in spurts.
this is the buzzing noise when speaker is idle, even when it isn't plugged into any audio source.
If this were ground loop interference, I'd expect it to be constant.
This only started recently. These speakers are 22 years old.
I hope someone here knows this noise and how to fix.