Via Engadget:
a bill expected to be introduced in the U.S. House of Representatives demands that the U.S. Secretary of Transportation initiate a study to determine if a minimum sound level is in fact needed and, if so, require that automakers comply with it (possibly as early as 2010).
As AutoWeek reports, the bill was apparently prompted by concerns that hybrid and electric vehicles are a little too quiet, and pose a risk to pedestrians, especially the blind.
I hope this idea dies quickly. My favorite thing about the Prius is the smooth and quiet ride. If this ever becomes law, I will disable the noise maker if my next hybrid or electric car is forced to have one.