Why carpet hides the cause but not the noise
Carpet is soft, so people are often surprised that a carpeted floor can squeak at all. But the noise was never coming from the flooring surface. It comes from the subfloor beneath, where a panel or plank has separated slightly from the joist and rubs against its fastener as the floor flexes. Carpet and underlay absorb some of the impact sound of footsteps, which is why a carpeted room can feel quieter overall, but they do nothing about a friction noise generated below them. In fact carpet frequently makes a squeak more noticeable by removing the competing sound of a hard floor. The upside is that carpet makes this repair easier rather than harder. On a hardwood floor, any from-above repair has to be made through a finished surface where the point of entry will be visible if it is not done carefully. On carpet the pile closes over a small entry point completely, which means we can reach and refasten the subfloor without lifting anything and without leaving a visible mark.