Impacts from hitting a wall during a rescue mission
Knocking two coffee cups together
Metalic tapping, some background air
Person walking up to the cockpit door, knocking, opening the door and standing in the doorway
Knuckles rapping on glass window
Knocking on cockpit door and then opening it
A wooden bathroom door being pounded 5 times impatiently .
Professional espresso machine - tapping portafilter three times.