Even if this were a bike from a shop, I'm not sure you could make a case for it being a warranty issue. Seven months of riding is a lot and stuff wears out. I've put this down as normal wear and tear. Quite likely the cones are pitted and need replacement. Replace the bearings while you are at it. It's a simple enough repair and probably not worth the hassle of returning the wheel in the first place. It may even be something as simple as the cone tightening because it wasn't locked against the outer nut properly.

Spend $10 to fix it or spend $200 in time effort and loss of bike while you get it warrantied...your choice.