 A lot of times heat builds up, and that heat dissipating from the brakes is what that squeal you hear. Now, there's a couple ways around it, okay? Every set of brake pads, if you have brake pads and rotors, every set of brake pads has what's called a hardware set. And that hardware set wears out. And a lot of times when mechanics do brake jobs, they don't replace the hardware set. They use the hardware set over again.