When I turn Voice Control, my external speakers begin to have high frequency distortion
As soon as I turn this on, I get the distortion. I recorded the sound where I turn this on and off so you can see what I mean -- HERE. Similar things happen during Zoom/GM calls when I turn on my bluetooth headset with a microphone, so it has to be on a line of sound input.
I have MAudio FastTrack Pro (which is a very old sound card:) connected via USB to my Mac Mini. Maudio is connected to Yamaha Monitors Speakers via large jacks.
MacBook Pro 13″, macOS 10.13