As is typical of building, blemishes tend to show up more clearly after the project is finished, and repairs are more difficult.
In this instance a floor squeak was observed in a bad location. Diagnosis of the squeak is fairly easy, but the cure can be tricky.
First the carpet and pad is pulled back and solutions are considered
A careful cut is made for further exploration, and a diagnosis of the squeak can now be made.
A block is inserted and the floorboard that is cut out can now be fastened with deck screws. The squeak is gone, carpet can be stretched back in place.