The lens hood shouldn't do that. Just curious, do you have more than one filter on the lens, or perhaps a difference/larger filter than normal (UV + CPF?)? On the wide side of many zooms, if I have a thicker filter, or perhaps stack ND's, I'll get a touch of vignetting from the filter edge. It doesn't look like flash shadow as that should extend across the entire bottom edge, thought the bottom right photo may exhibit some of that. IMO it's definitely either the hood (which should be sized appropriately not to do that) or a filter edge.