I had the same problem on this project. servo is making interferences that are readed as knocks and open the lock.
Servo buzz can come from two thing:
peak impulse when starting the servo, solution is putting an electrolytic capacitor, at least 100 uF, directly across the power supply to the servo.
I tried it and it didn't change anything.
second solution: "cheap servos don't know how to stay at the limits of their movement very well, which can cause the buzzing/shaking you're mentioning. However, if you just limit their range to 10~170 degrees, the issue will be fixed."
I did it and it worked!
So the servo bundled in the arduino starting shouldn't be used at limit positions.
all credit to http://electronics.stackexchange.com/questions/77502/is-there-a-way-to-stop-servos-from-shaking where I found thoses answers