A buzzing garage door could have a malfunctioning transformer inside the motor. The gears inside the motor could also be stripped. \
Over time, the teeth on the gears wear away and the gears become stripped, so they no longer turn. The gears spin and spin, which creates the moise. \
Broken torsion springs can also create a buzzing noise as the gears attempt to pull the door up and down without springs, which puts a strain on the motor and creates the noise. If you continue to attempt to open and close the door with broken torsion springs, you will strip the gears. \