I am making progress! I have discovered that the problem is ONLY pesent when I have audio cables plugged into the Kurzweil (and octa, of course). Interestingly (to me) the Kurweil does not even have to be powered on for noises to appear at the monitors. If I unplug the audio cables from the Kurz - SILENCE! - even if I have Dim Pro running and using my Remote SL for midi input. Therefore, I have to conclude that the audio cables from the Kurz are acting like antennae for RF interference. I have tried every audio cable in my arsenal (nearly all are unbalanced but there was one short pair of balanced cables). Some are better than others, none are perfect. The balanced cables I thought might be the solution but they are no better than average. That said, they are probably pretty cheap balanced cables. I really don't even know what I ever bought them for. So, unless someone has a better suggestion, my next step will be to get some decent balanced cables and see what happens! Once again, thanks for all of the suggestions!

Time to summarize. Over the past 10 or 12 days I have totally taken my system apart and reassembled. I have looked inside the computer and found a massive tangle of wires but nothing I can really do anything about because it is a very tight mini-tower case. I have changed over to all balanced cables for audio. I have removed the Octa from the same cabinet that holds the PC. I have paid attention to cable nmanagement and minimized power and audio cables in proximity to one another. And STILL I have noise. As mentioned earlier, grounding the Octa to the PC did help somewhat. Also unplugging audio outs from the Kurz silences everything but iis obviously not a great solution.  Also, grounding the Octa to the Kurz chassis does nothing BUT grounding it to the metal on the outside of the balanced audio cables at the Kurz outputs results in SILENCE! (better than grounding to PC). So, maybe it's not rf picked up by the cables but some sort of grounding issue between the Kurz and the Octa?? (Obviously I am ot an electrical engineer!). For now, I am grounding the Octa to the audio cables at the Kurz which sounds good but looks weird! I remain open to other, better solutions!

I think you just have dirty power coming from your wall outlets. A proper USP that filters the power is your best bet if you can't get an electrician in to check things out.

You should NOT be getting that much noise... period. Good luck.

Also unplugging audio outs from the Kurz silences everything ...

If you're unplugging them at the Kurz then it's possible there's a fault in the Kurz generating noise or the Kurz is what is picking up the interference - does the noise stop with the Kurz plugged in but powered down?

Powering down the Kurz doesn't really make any difference. Unplugging the Kurz quiets things down a little bit. Thinking that the Kirz might be the whole problem. Possible that there is some sort of ground issue with the Kurz that is causing all this. The noises are definitely coming from the computer (moving the mouse makes an obvious zipper sound, the rest is sort of a rythmic chick-chicka-chick kinda sound) but the are only there when the audio cables are touching the outputs of the kurzweil. BTW, I know it isn't the Octa because I had the same problem with my old m-audio 410. FWIW, the system is all plugged into a Furman rack rider power conditioner - I don't know if that makes any difference at all in terms of power quality.