If the squeak exists only in the flooring, try applying some powdered graphite into the seams. In most cases, once it works its way in, the annoying sound will stop. If, however the floor has too much give or movement, drive flooring nails or screws into the floor and fill the hole with wax wood filler. Use screws designed especially for this purpose. Once in place, the heads break off so as not to be exposed.