If it's on the outside where the arrow is pointing I really don't see how that could be a vane hitting it.
None the less, paper tune your bow. That will show any fletching contact right away. Also , check the vanes to see if there are any kind of marks on them. You could also powder test if you don't have access to a paper tuning rack.
I have only seen fletching contact only on the prongs and not on the rest itself.

Do you shoot w/ cock vane down?