Pull off the deck belt and check the spindle mounting .
If there is any movement in any of them, take it back and start a warrantee claim.
A loose spindle ( which should have been checked predelivery ) can cause the blades to touch which in turn can cause the spindle to bend or the housing to crack.
Taken back now if there are no chips or gouges in the blades ( indicating you hit something ) which would trigger an owner negligence response and you will start a warrantee history so if you have more deck problems a bit latter on you have a fighting position.
Grasshopper from what I have heard are really good warantee wise.