With early data now showing that hybrid cars seem to hit pedestrians more often, carmakers are ramping up efforts to find ways of alerting people when a nearby car is operating in electric mode.
Now the UK's Group Lotus Engineering has come up with a noise-generating system, one of several approaches to noise-making equipment for electric-drive cars.
Its HALOsonic External Electronic Sound Synthesis system creates a range of different noises, from a droning buzz to simulated exhaust sounds from a variety of virtual engines.
Their reversing ping sounds particularly annoying, and we're not quite sure they've nailed the "American V8" exactly. But their two "futuristic" options make their second-generation (2004-2009) test Prius sound like something from a science fiction movie.
Which made us chuckle if nothing else.
The video below shows the Halosonic system in operation. We'll let you decide whether this is something you would want to add to your own Toyota Prius to address the lack of noise when it's running in pure electric mode.
The need for audible warnings will become even more acute with the arrival next year of the 2011 Chevrolet Volt, which can run 40 miles on electricity from its battery pack.