Could be brakes (does it only make noise when brakes are applied?) or a wheel bearing.
Like I just said in another Mazda thread, many dealers will try to squeeze all cash they can out of a client before doing what they are supposed to in such a case - inspect, diagnose and repair under the manufacturer's warranty.
I would talk to Mazda and express my dissatisfaction with such approach. If even that doesn't work, which is unlikely, then an indie mechanic is your next stop.
