Silent Hybrid Danger

You can never win in some situations. With hybrid electric-only mode cars, normal “car noises” have been significantly reduced. As is such, the issue of pedestrian and cyclist safety has been brought up. So the debate has begun. To add an artificial sound to hybrids to alert sluggish pedestrians, or to use it as a start to forcing them to take more responsibility while on the road. Hybrids emit less than three decibels of noise starting up, a level hard to pick up with the human ear. One traveling at 35mph will emit a sound as loud as a vacuum cleaner. What kind of compromise would everyone have to reach to solve this would-be problem?