Various reasons can contribute to squeaks. Squeaks can be installation or site related such as an unlevel subfloor or even environmental. Environmental squeaks in hardwood can be lessened by maintaining correct temperature levels of 60-80 and humidity levels of 30-50%, before and after installation. Because of the needed tongue and groove system in wood flooring, squeaks are bound to happen and are viewd as normal. However a persistent or excessive squeak found can be pulled down from underneath the floor by using the correct screw length. Also, try applying baby powder topically into the groove right at the squeak, it's less invasive and you may fine that it was all that was needed!