I was wrong about the switching frequency setting. The Ubox is actually set at 40kHz! I turned it down to 25 kHz and set “Sample in V0 and V7” to true. It does seem to have reduced the problem. It’s more of a whine than a blood curdling scream, and it doesn’t last as long. Before it lasted clear from 25-30mph. Now it seems to be right at 26 mph. I’ll do some more science, but I may owe Flipsky an apology.