What about those spy cameras, not to mention the chem-trails from them other flying dudes.
I love the deep reverberating sound of a Bell 412 air ambulance on a still night as it heads towards the nearby major hospital. Its sound is dutiful and purposeful as it executes its role of giving the guest in the back seat every possible chance of an extended life. Unfortunately head trauma victims require a style of flying that can upset the uninformed on the ground.