After the latest rear tire change, there was a constant rattle coming from the rear wheel. We made sure the main nut was tightened to spec, and the noise went away. After a few hours of riding the noise came back. Checked the wheel, there was some side to side play in the wheel. Checked the nut, it was loose (or at least not within spec). Retightened, noise went away. Next ride of a few hours, the rattle is back.
Why won’t the nut stay tight?