Alpha,
You say surging, but you do not give any hint to the frequency of the cycling. One of the things that digital system all have as an issue is the interaction with other digital system. This can lead to either aliasing (displaying something that is not as it should be) or phantoming (not showing something that is actually there). Either would be possible in this case. Whether one of these is what is happening can only be determined with instrumentation I doubt you have. You may not be able to determine whether it is caused by the PD9280 or the H2Ki.
As I write this I have been trying to think how to isolate and or eliminate the problem, but without knowing which to change. The only thing that would be simple won't be easy. It would require getting your hands on a line conditioner, I may have one of the few surviving examples. Just an isolation transformer might do it, but it would have to be about a 1Kw size to support the PD.
Matt