Brakes squeak in disc brakes because this is caused by vibration of the rotor, pads and caliper. Performance brakes will usually have a higher concentration of metal in the pads. This increased metal content will sometimes allow, or even cause, more vibration than the older organic, asbestos and first generation semi-metallic brake pads. In performance brake pads, the bonding materials that the metallic pieces make up the friction material in a brake pad, is also more durable than with lower performance pads/ This increased durability also contributes to the squeak, causing vibrations. Beveling the edges of the brake pads and using silicone adhesives when installing the pads can alleviate this squeaking.
For more info, see How a Carbon Brake Works