It could either be brake dust causing the squeak, or it could also be the brake pad sensors. The built-in sensors squeak when the pads reach a certain low point.
Squeaking brakes is caused when the brake pads become old, rusty, and eroded. This results in the vibration of these pads on the calipher assembly, in an area called the mounting clips.
If they are brand new, they are just wearing in a bit. However if they are not new, you should check the thickness of the pads. Squeaking is usually caused by the squealer or just the metal plate scraping the rotor.
Usually the weather is the main cause because when it is cold the brakes squeak. Another cause could be dust on the brakes. This causes them to sqeak pretty badly.
If your brakes squeal then they may need replaced. Pull them off and make sure the are worn down. If they are fine try apply a small amount of silicone or copper grease to the back of the pack to quiet them down. Also make sure you are missing any clips.
