Seems a bit obvious, but some of you may have missed it. The Greyjoy's main island(s) is called Wyk. "Vik", in Norse, means "inlet", and is the source of the name viking. In fact, I remember reading somewhere that the vikings got their name specifically because on one of their first raids, one of the survivors said they were men from "Vik" (which is also a region in Norway).
Now take this, along with the german language custom of "w" being pronounced "v" (Richard Wagner, for example). Plus, it seems to me that GRRM likes to replace "i" with "y" quite often, just to add a bit of exocitism to his stories (Raydar=Raider, Wyk=Wik, Arya=Aria, plus dozens of others I'm sure I'm forgetting).
