This looks like "b-roll" footage provided by GM and meant to be spliced into news reports about the Volt, where the volume is usually cut out.  I saw the first chunk of this video on YouTube a few days back, and didn't think the car sounded loud (though the sound was "unrefined").  This version of the video does seem louder for some reason...  But, since the only point of reference for sound is that lady going in and out of the house, it's hard to say if my headphones are just at the wrong level.

Still, my understanding is that the prototype on display at the auto show isn't actually functional.  This thing likely has some random motor thrown in, possibly with significant gear reduction to get enough power to the wheels (it might just be a lowly 5hp motor or something).  Whatever gears are in there might also be temporary and not "broken in" or there just might not be any sound deadening in the vehicle yet.

The "conspiracy" is simply that the vehicle has only been in development for less than a year and still has years to go to reach production.  Like Ryan said, they're just showing off the body in the video, and demonstrating how customers would plug it in every day.