buzzing auto door locks

my cousins 99 durango just started to act up. when the auto door locks at 15 mph or 2nd gear, whatever it is. it makes a buzzing sound that pretty loud. can anyone help me out on that. we are trying to fix it and not sure what it is. sorry in wrong thread, just dakota and durango have the same stuff. thanks

the power door lock actuators

and what do i do about fixing it