Hi Kathy, Many times the squeaks are caused nails, usually shot by a nail gun, that missed the joist below or glanced off the joist, and thus moves up and down when you walk over it, causing the nails to go in and out of the wood or rub on the joist, and ultimately causing the squeak. You could try to screw the floor down to the joists at the locations of the squeaks, but is not a guaranteed solution. If you have carpeting, there are special screws designed to be screwed THROUGH the carpet and then broken off below the surface so not to damage the carpet. If you have hardwood floors, the squeaks can be caused by nails, which are driven through the tongues and are not visible on the surface. Over the years, the nails may lose their grip and move up and down in the subfloor, again causing a squeak. This can sometimes be remedied using graphite, which when squirted through the cracks in the flooring will lubricate the nail and cause less friction. Sometimes, it is necessary to drive finish nails straight into the hardwood, as a last resort. Finally, a good number of squeaks in newer homes may be the result of swollen particleboard underlayment that was installed too tightly and rubs BETWEEN each joist as you walk over it. The only cure for this problem is to pull up the carpeting and run a saw down between each sheet of underlayment, thus eliminating the rubbbing. As for installing the "I flooring" you mentioned, that is not an option unless you plan to do major remodeling. Those are actually I-joists, and are quickly replacing standard lumber joists which were used in the past. There is no flex in these joists and the wide flange on the top allows for a greater nailing surface, and thus eliminates the squeaks caused by missed nails. I hope I have helped you understand this frustrating problem so many people, including myself, suffer from. Good Luck.