As long as you can access the floor framing, you can hush up your floor in minutes!
Polyurethane Construction Adhesive
Fill the Gap
Locate the floor squeak and inject polyurethane construction adhesive into gaps between joists and plywood. Make sure to ventilate the area.
Smooth the Bead
Push the bead deeper into the floor gap with a plastic spoon (because it's so sticky). It's also easier to wear gloves, so you can just throw them both away when you're finished.