It's probably the cheap mdi -> usb cable.
try something like this, get the right size:
I ran into this problem when using a sennheiser mkh70 near a physics lab once. Talked to the manufacturer and they suggested ferrite clamp-ons like these on the cable to help resist RF. I haven’t had the same problem again so it’s hard to say how much effect it has but might be worth throwing a few in your kit (OP) in case it happens on set. Also you now know what sorts of objects to look for and turn off if you run into that sound again in the future.