Braking noise on 1997 GMC 3500 Pickup

somtimes as I'm driving, such as in parking lot or coming up to stop light, brakes start making noise like cow, weird mooing noise. My truck has hydro-boost unit. What could this be.

Asked by for the 1997 GMC 3500 Pickup
Your brake pads are worn out. Make sure to change the break pads quickly or it will damage roter.