Measured voltage levels on my dragon's lair

So Warren suggested that I measure the voltage levels on my Dragon's Lair hardware to troubleshoot my monitor's problems that were evident in the video from yesterday. I just did. It's a little hard to tell for sure, but I believe that there is some A/C interference going on. I measured the voltage between the power supply's metal piece and the monitor's metal frame which should be 0, and it definitely did not seem to be steady at 0. It seemed to be fluctuating a bit between 0 and 0.02V but since it shows an average I couldn't tell for sure. I did measure the voltage going to the NTSC decoder card and it is a solid 18.6V (supposed to be 16V). I don't know what to think about that.