Over time, due to stress and dirt, bicycle pedals can begin to creak or make other, less definable noises. The problem may be as small as a loose spindle in need of tightening and a little grease, or more serious, such as dry bearings grinding against one another. Unfortunately, pedal noises are not indicative of any specific problem. To fix your pedals, begin with basic tightening and cleaning, and then progress to greasing the bearings.
Clean the pedals
Unscrew the pedal spindle from the crank arm. The crank arm is where the pedal attaches to the bike. Some pedals will require a hex key to loosen -- the hex head bolt will be at the back of the spindle. Other pedals will require a pedal wrench. These pedals are loosened at the point where the spindle enters the crank arm. Remember -- non-drive side pedals are reverse-threaded. Turn them clockwise to loosen.
Grease the threads of the spindle liberally. Clean any old grease or debris from the crank arm threads. Wipe dirt and grime from the pedals themselves.
Re-attach the pedals, wiping any excess grease from the spindle. Test the pedals to see if the noise has stopped.
Grease the bearings
Remove the pedal and place the threaded end down in a soft-jawed vice. If you do not have access to a vice, hold the pedal steady with your hand.
Pry the dust cap from the top of the pedal, using the blade of a flathead screwdriver. There will be a locknut underneath it.
Loosen the locknut, using an appropriately sized spanner wrench. Hold the spindle in place with another wrench while turning the locknut anti-clockwise. Remove the locknut and the lock washer behind it. You will now see a cone, which holds the bearings in place.
Unscrew the cone and remove the bearings inside with a pair of tweezers. Turn the pedal over and pull the spindle out.
Remove the second set of bearings, just as you did the first set. Pack medium-weight grease into the bearing cups, and reinsert the bearings one by one. Reassemble the pedal.
Remember the order of bolts and washers when removing them from the pedal. Alternatively, use a piece of string to thread through these items as you set them aside. This will help keep them in order.