Try having a synth studio in the same room as a ham radio shack. It's a battle, but I have conquered RFI (radio frequency interference)... I won't go into details because everyone's situation will be different for different reasons.
But, I can tell you to research ferrite chokes, common mode chokes, and double check all your wiring when you've got a Theremin inside your studio.
I would advise you to keep the Theremin (power cable and audio cable as well) as far away and isolated as possible from ANY electronic equipment.
A Theremin is a miniature BROADCAST radio station inside your room. It can effect lights, your mouse, keyboard, computer, and possibly other synths.
My best advice to you would be to purchase ferrite chokes for your power cords, and keep your thermin as far away as possible from anything vital in your studio.
Choke out that RFI. The Theremin can effect USB cords, USB hubs, your monitor, etc etc etc...
Ferrite chokes, cable isolation, and physical distance (isolation) will be your best bet to rectify your unique situation.
Also look into grounding your Theremin and or MicroFreak. It can't hurt.
If you can't figure this out yourself, then find a competent electrician, and hopefully he can solve your problems.
Good luck 🤞