Newbie question, strange rubbing/grinding noise.

Hello all, I just picked up a 2010 Prius model V from my Toyota dealer here as a Certified Pre-Owned. On the test drives I noticed a slight rubbing, (almost grinding) noise at slow speeds. I don't know enough about the hybrid setup to imagine what it could be, but it sounds like a muffled wheel bearing sound. The dealer has looked at it twice already before purchase and assured me that there are no problems with the brakes, nor the wheel bearings. I've taken delivery and the sound is still present and I will be taking it back in tomorrow. Any ideas on what it could be? I'm just concerned that it could be related to the CVT. I am covered currently by a 12month/12,000mile bumper to bumper, and a 7yr/100,000 mile power-train warranty so I'd like to get it taken care of as soon as possible. It just broke 47,000 miles. Any advice is appreciated - thanks.