Two pieces of wood rubbing together are the cause of most squeaks in wooden floors. There are two reasons this happens. In one case the wood floor has pulled away from the subfloor that lies beneath it. Most hardwood floors are installed by nailing the wood floorboards to a plywood subfloor which rests on the support beams underneath. The subfloor can warp or the nails used to secure the floorboards in place come loose.
The second reason for squeaks is a gap between the subfloor and the joists. The gaps most likely occur because the subfloor has warped. Real Wood Floors recommends finding a quality wood floor contractor in your area to evaluate your floor to discover where and why the squeak is occurring. Most likely, it will be something they can fix quickly and easily. Their are several kits a wood floor owner can purchase online, however, most of these kits are not effective or only mask the real problem.