Hammer knocking a dull surface, fast
Sharp wooden impacts or wooden axe cuts.
Tapping of a percussion instrument that varies in pitch
Knocking on a wooden surface or door.
Several glass bottles rattling , knocking together
Person walking up to the cockpit door, knocking, opening the door and standing in the doorway
Metal being hit or struck, soft impacts, x2
Knocking on cockpit door and then opening it
Dropping a cardboard box or on the floor.
Professional espresso machine - tapping down portafilter once.