A squeaky bicycle seat might not seem like a big deal at first -- until you pedal along, racking up the miles, and it becomes more annoying with every passing minute. If the squeak goes away when you stand on the pedals, you have a fair amount of evidence that the noise emanates from the seat. Your work to fix the squeak needs to address the components of the seat: the saddle and a pair of built-in, thin metal rails underneath the saddle.
Spray lubricant where the seat rails run through the saddle clamp, which sits atop the seat post and holds the seat in place.
Wiggle the saddle. If it is loose, tap the nose of the saddle up or down to level the seat. Hold the saddle in the correct position. Tighten the clamp with an Allen key or wrench.
Test-ride the bike. If the squeak has gone away, you are finished. If the squeak remains, continue with more in-depth maintenance.
Use a wrench to loosen the binder bolt, which holds the seat post in the frame, or flip the quick-release lever that holds the seat post to the bicycle frame. Remove the seat post and seat as a unit.
Grease the threads of the binder bolt and outside surface of the bolt where it touches the frame.
Loosen the seat clamp with an Allen key or wrench until it opens enough to readily slide the rails forward and back. Repeat your earlier spray lubrication of the seat rails, this time oiling them along their entire length, including where they meet at the front of the saddle. Lubricate the areas not accessible when the saddle clamp is fully tightened over the rails. Tighten the clamp.
Insert the seat post into the bicycle frame, and tighten the binder bolt or quick-release bolt. Check whether the saddle is level. Loosen the seat clamp, level it and retighten the clamp if necessary. Test-ride the bicycle. If the squeak persists, you might have a welding joint failure in the seat rails and need to replace the seat.