RFI, Radio Frequency Interference. It happens on many things, telephones, your sound system. You must have a radio station close by.
In days of old before cable, and it can still happen rarely with cable, when someone with a CB drove by it would come thru on the TV. Cars also used to drive by and you could hear and see the interference from the vehicle ignition on the TV.
Ever had a remote control car act weird when no one has the remote. It's a CB radio.
You might try some ferrite beads on your power line. Maybe on any interconnects. You can get them at RS.
In days of old before cable, and it can still happen rarely with cable, when someone with a CB drove by it would come thru on the TV. Cars also used to drive by and you could hear and see the interference from the vehicle ignition on the TV.
Ever had a remote control car act weird when no one has the remote. It's a CB radio.
You might try some ferrite beads on your power line. Maybe on any interconnects. You can get them at RS.