Hyundai Repair: 2007 Sonata full tank, gauge readings, empty boxes

Question
I recently bought a 2007 Sonata.  I recently moved, so I had some empty boxes in my trunk.  I'd hear what sounded like boxes rolling around back there, so I didn't think anything of it.  Now that the boxes are gone, the noise continues, but only when the tank is relatively full.  Should I be worried?  Is the tank not secured properly?  Should I take it to the dealership?

Thanks for your help!

Answer
It's possible you just hear the fuel sloshing around; there are no baffles in the tank to prevent this.

But I've also seen one car where the fuel pump assembly had broken loose from the mounting plate and was knocking around in the tank.  Since the fuel sender is attached to the pump assembly, I'd expect erratic fuel gauge readings if this were the case.  If that's the case, definitely take the car in for service.  If not, it's probably just the fuel sloshing around.  Even in this case, you may still wish to take the car in just for verification that there's no actual problem.