here are a couple different reasons why a disc brake would create some undesirable noises while you are out riding. Let’s take a look at a few of those..
Properly bedding brakes in: Improperly bedding brakes in can lead to uneven braking as well as noisy brakes. It is important to have an even braking surface from the beginning in order to gain the best braking performance possible as well as eliminating any premature noisy brakes.
Misaligned calipers: It is possible to have your brake caliper get out of alignment, this can happen right out of the box, after riding if the bolts become loose, If the caliper is bumped by another object. Luckily this is a pretty simple thing to address. You can loosen the two post mount bolts that hold the caliper on. While compressing the respective brake lever you will retighten each bolt by a quarter turn at a time this will ensure both bolts compress the caliper at an even torque. This should allow the caliper to self center onto the rotor and should align things. You may have to repeat this process a couple times as there is limited tolerance to work within, so you don’t always get it the first try.
Possible contamination: The braking surfaces found on today’s modern disc brakes is extremely sensitive to any outside contamination which can lead to terrible sounds and poor braking performance. In order to reduce the likelihood of this dreaded condition it is recommended to avoid touching your brake rotors without some sort of protection like gloves or a shop cloth. The oils on are skin are enough to cause pesky noises, lubricant and grease can be an even more fowl contamination possibly requiring replacement of both pads and rotors. If there is a minor contamination however we can get lucky and with rubbing alcohol and sandpaper can fix this issue. You will want to remove your brake rotor and allow thoroughly cleaning with rubbing alcohol. We will also pull the pads out and sand these down in an attempt to get down into the braking surface and remove and possible oils that have soaked in. From there you can reinstall the components and properly bed the brakes in to maintain an even clean braking surface.