All sounds CC-by-sa Julien Jorge, produced with the following samples.

dropping:
CC-by Pullover aus Milch http://www.freesound.org/people/Pullover%20aus%20Milch/sounds/46419/
CC-0 batchku http://www.freesound.org/people/batchku/sounds/10352/
CC-0 cognito perceptu http://www.freesound.org/people/cognito%20perceptu/sounds/17468/

propeller:
CC-by nofeedbak http://www.freesound.org/people/nofeedbak/sounds/41171/

trap-door-closing:
trap-door-opening:
CC-by NoiseCollector http://www.freesound.org/people/NoiseCollector/sounds/57023/
CC-by AGFX http://www.freesound.org/people/AGFX/sounds/42937/
