I thought I was hearing some strange noises from my rear wheel, so I put it on the truing stand to see what was up. It was still true, but I was shocked to realize that I hadn't crossed one of the spokes. It is a 32 hole Velocity Synergy. Many thousands of miles on this wheel.
I am tempted just to loosen it and cross it. The purist in me says to loosen the whole wheel. It's on the NDS, which probably explains why it didn't have much effect.