Hum in Speakers with New Dedicated 20 amp Circuit

I color coded it. Yellow is the coming wire. Black hot. White is neutral. Green is ground.

Forget the color-coding. Competent electrical people can figure it out with a simple text label.

This is how it should be done.

And just what do have that requires 20A continuous / 200A peak?

mjjw: "The sub panel has been in for almost a decade."

The panel is illegal.

Insurance companies love illegal and uninspected installations 🤑

I haven’t checked the code in a while, but I think it’s because a panel is more or less permanent.

With an outlet, if it’s out of the box, no earth. Gotta protect the unskilled from themselves.

Looking at the photo again this morning of the feeder conduit entering on the left side of the panel it may very well be PVC conduit.

I concur looking at the color, saturation and reflectivity of the visible threads. It's a very close match to the PVC exit.