Okay, Arduino-0018 did no good at all, so I returned to 0022 and started looking through the core files to see if anything looked wrong – not that I’m any good reading someone else’s code. On a guess, I deleted all the Sanguino core files, except pins_arduino.c and pins_arduino.h. Then I copied all the other Arduino core files to the Sanguino core directory. Now, I’ve got a nice, quiet servo!
Although this procedure solved one problem, it may introduce others as my program expands. Still, I’m confident enough to proceed with a circuit board.
Jon