Al and Davide really helped to solve the puzzle.
As mentioned above, I thought a simple reboot addressed much of the problem, but I finally had time this week to remember and take a closer look at the power and "sleep" settings.
Wow - that made a huge difference and really seems to have eliminated the problem.
Why computers would automatically do that with such bad side effects on performance without disclaiming them makes me crazy.
Why not set a machine for proper performance, and then be able to choose maximum battery life, while understanding that certain functions may suffer?
(But then again, I suppose most of the world thinks MP3 and iPod earbuds sound good.)
Later, I hope to spend more time with the geekier aspects of configuring PCs for audio as described in the DCS article.
IN the meantime, worrying about jitter, RFI and outlet power before changing the sleep settings, was a bit like wondering if I was using the right amount of spice when there was a dead rat in my soup.
Thank you all for expert advice as usual.