Brake squeak is often the result of older brake pads, but can generally be fixed with a few simple steps. While the sound of squealing is very unpleasant, it is also an indicator that your braking system is aging and needs adjustment. Sometimes, even brand new bikes with cheap brake pads can squeak. Luckily, this can often be solved by taking the same steps to diagnose and fix the problem.
Look at your brakes from above: do the pads hit the rim all at the same time? If so, toe them in by adjusting them so the front of the pad hits slightly before the back. On a modern brake this is easily done once you loosen the pad mounting. With older brakes you will need to twist the arm of the brake caliper.
Remove the brake pads and inspect them: is the surface shiny? If so, metal shavings from the rim have embedded themselves in the rubber of the pad. Take some sandpaper and rough up the surface of the brake pad. If you bought a new bike online, and after it arrived and you assembled it you discovered that the brakes were squeaky, you can use this same technique to sand down the face of the brake pad so that the surface area is more receptive to the braking surface of the rim. Also try switching the left pad with the right pad to see if that helps.
If you still have squeak, the rubber in your pads might've hardened. This can happen with time, or by being exposed to oil. You'll probably have to replace them with new pads. We suggest taking them to your local bike shop to get the new pads and have them professionally installed. This should cost around $20 and ensure the greatest satisfaction afterwards.
Hopefully this helps article helped you understand why brake squeaking happens on a bicycle, and some easy steps you can take to relieve it! If you have any more questions about how to fix squeaking brakes, feel free to hit us up anytime!