Reverse thrust :
I've met more than one person who thought that reversing the engines was done literally - that for a few seconds the inlet air was now drawn in at the rear and the exhaust and thrust went out of the front. While this might amuse the regulars here, it is what a lay person could feel was the obvious way to do it.
Likewise reverse pitch on a propeller plane being thought to be achieved by turning the engine in the opposite direction, issues such as variable pitch being generally not understood. I attempted to draw a comparison with a car's reverse gear, only to be told that this did indeed "turn the engine backwards" when selected.
General noises :
One of the most amusing I recall was in a BAe146, Euromanx, London City to Isle of Man. In the cruise, suddenly a quite noticeable "Kerboinggggg" twanging-spring noise from the cabin wall, like the sort of silly noise The Goons used to specialise in. I guess there was some spring-activated device inside there which had suddenly operated/let go. Any 146 engineers hazard a guess at what it was ? !