Inspect the inside of your box spring for a broken spring or a loose part. If you have a box spring with a cloth covering, you will need to cut part of the cloth with scissors to get inside the box spring. If the problem is a broken spring, cut the spring with a pair of pliers. Throw out the broken part once you have cut it. Removing one or two broken springs will not harm the quality of the box spring. Also, some box springs have screws in strategic places. Use the screwdriver to tighten any loose screws. Test the box spring by pressing on top. If this solved the problem, sew the box spring cloth as best you can with a needle and thread. If you cannot sew it, you can use a dust ruffle to hide the open space.
Oil your springs with WD-40. If you haven't already, cut the box spring cloth with scissors. Make sure you have a drop cloth around your bed or under your box spring to catch any dripped oil. Oil all the springs. Wait a few minutes for the oil to saturate the springs, then test the box spring for a squeak by pressing on it.
Place a foam mattress cover between the mattress and the box spring. Sometimes buffering the mattress will reduce noise from a squeaky box spring. Also, you can buy furniture pads or coasters for the feet of the bed. Place the furniture pads under the feet of the bed, and sometimes the added padding will reduce squeaks when the bed is moved.