What kind of interference is this?

[Jon1967us]

Aside from the obvious horizontal pulling issue, is the apparently diagonal pattern of little dots shown in the below video what they call a 4.5 mc beat pattern? I'm not able to find much information or examples that match by googling.

I have the signal coming in from an off the shelf converter into the antenna terminals. TV is powered from an isolation transformer.

Not sure where this is coming from. I checked the heater to cathode resistances on the tubes, other than the audio and tuner, and no shorts found. However on a couple of tubes there are 2 instances of resistances between heater and cathode being 7Ω and 10Ω. Could it be a leaky cap to ground along the filament string? The only suspect I can think of would be a ceramic along that line just before one of the suspicious low resistances.


https://www.youtube.com/watch?v=bL0HkjeImIE