Hipot interference

[mkwired]

For most of this week, I spent troubleshooting a torque testing machine that I developed.  The system includes a "microcontroller board", a stepper motor controller and motor, a torque meter, and a computer.  I quickly fixed all the small problems, but I kept having an intermittent problem where the microcontroller board (Arduino Uno) would stop responding to the computer.  The two are connected using a USB serial connection.  I found out that the Hipot testing that was happening a few feet from me was causing the problem.  Whenever they abruptly shut off the high voltage, the USB connection would stop working.

I have attached a picture of the bench with the equipment on it and a screenshot of the electrical impulse that is being created by the Hipot tester.  Can someone explain what is going on?  The magnitude of the impulse seems only to be affected by how close or far the oscilloscope probe is from the high voltage lead.  The scope isn't part of the setup.  I'm only using it to see the affect the Hipot machine is having on the local environment.