Can anyone help me diagnose this? I've also xposted it to applefritter. 

In this linked photo you can see a rolling "interference" through the display.

This only occurs when the //c is on, but not while just the Monitor //c is on.

It does appear to be more shaky and will distort the text characters on floppy read/write.

Is there a filter/capacitor/component that is responsible for this type of effect that I could replace?

Thanks!