I've had 3 V's in the last 3 years, 2011, 2012, and now a 2013. I experienced the very same thing on everyone of them. By the time the second one rolled around I had figured it out. It was loose lugnuts. The way I figured it was on the 2011 it stopped after I replaced the tires at 20K miles. I knew the tires were not capable of making the noise.

So when the 12 started ,making the noise I took it around to my shop guy and asked that he tighten the lugnuts, noise gone.

So now I'm on the 2013 and it has about 5K on it and it just started doing it and I plan on getting the lugnuts tightened again.