If your hardwood floors are squeaking when you walk across them, there's no need to tear them up and replace them. As a house settles and wood dries out, it's normal to begin hearing squeaks and creaks. The noises are caused by two subfloor boards rubbing together, loose nails or tongue-and-groove joints rubbing against each other after the wood has dried. Squeaks and creaks can be fixed.
If squeaks are coming from an uncovered wood floor, try this quick fix.
Use a talcum powder---baby powder works well---and sprinkle a bit into the joints where the squeak can be heard. Let it settle, place a piece of newspaper over the area and step on the boards to move the powder deeper into the joints. Remove paper, then sweep or vacuum the remainder.
That should take care of the squeak. If the squeak has not disappeared, you'll have to take different measures.
If you can reach the wooden floor from below, try this fix:
Pinpoint the squeak by having someone walk on the floor above you. Once you've located the squeak, coat a wood shim with carpenter's glue. Tap the wood shim between the joists and subfloor. Use a drill to drive one 1/4-inch screw up through the joist and shim and into the subfloor; this gives added support.
When you don't have access to floors from below, it's still possible to fix a squeak without damaging your floors.
Pre-drill holes through floorboards, about 1/2 inch from the edge at an angle. Do not drill through the sub. Use a nail set to drive the nail heads below the floor surface, and fill the hole with colour-matched wood filler. Countersink each screw, using a countersink drill bit. Fill the screw hole with wood filler that is the colour of your floor to hide the screw head.
If you have installed carpet and you hear a squeak underneath, you can still eliminate the noise. Simply, pull back the carpet so you can reach the squeaky area and use one of the methods described above to fix the squeak.
Don't use nails or screws that are too big, because you could splinter the floorboard.