Plywood subfloor making squeaking sounds

Squeaking noises are made from the fastener not hitting the joist properly. Once the joists are covered with the plywood it is easier to not hit the center of the joist with a fastener. If it just about misses the joist when the plywood moves it will make a noise similar to a bow and violin as the fastener move in the wood. Another nail next to the squeak will stop any noise if it hits the joist securely. If a nail is driven by hand instead of using a nail gun, it will be easier to tell if the nail hits the joist.
If squeaking occurs after flooring installation an eight penny finish nail driven into the joist through the finish flooring will stop the squeak it if finds a joist.