Scott I have a couple thoughts for you quick as they maybe given that I am trying to go home! :-)
1) Is the interference line-locked? Try triggering off the line freq once... 2) Is the building`s electrical supply underground? What are the ground water conditions like around your plant now, given the time of the year (spring) and being located near a swamp? 3) If you suspect that there might be a feeder problem, your local electric company should have a interfence dept where they will come out and look (with receivers) for leaky insulators, lightning arrestors, cables or ect. Our 10m OATS site at Waukesha has had that very same problem. good luck, dave garnier ge medical systems ultrasound engineering 414-647-4286 ps: the xray tube operates for a very little time, given that most of the power (kilowatts) goes up in heat. The emc radation from the tube and cables would therefore be of vary short nature.