What goes wrong with hardwood other than noise
Squeaks are one failure mode. The others are mostly about moisture and wear. Cupping, where the edges of a board sit higher than its centre, happens when the underside of the flooring picks up more moisture than the top, usually from a damp basement, a slab without a proper vapour barrier, or a spill that reached the subfloor. Gapping is the opposite: boards shrink away from each other as indoor air dries out over a long heating season, opening lines you can see. Crowning, where the centre sits proud, often follows a cupped floor that was sanded flat too soon. Then there is straightforward damage, a board split by a dropped weight, a section worn through its finish in a doorway, or water staining after a leak. All of these are board-level problems, which means they are board-level repairs. Individual boards can be lifted out and replaced, and the replacement blended so the repair is not obvious, without touching the rest of the floor.