Assuming you've ruled out a mis-mounted lens hood, I'd say it's decentered and I'd exchange it.
Yes, I'd go for a replacement, except that I'm just sitting back and seeing how everyone is doing with theirs. So far, I've read about a lot of sample variation, which is a bit disgusting. I'd consider the Tamron, except it seems to have even more issues with QC.
Once you have found a good one, never let it go.