Pronunciation of "因为"
I wouldn't have believed you unless I checked it myself, but it appears these are both interchangeable with one source claiming:

http://www.askbennychinese.com/questions/detail/3713


  In fact, in the south of China, people says “yīn wèi”, while in the
  north people say “yīn wéi”. The only difference lies in the
  pronunciation. Basically, they are exactly the same.


My wife and most of my friends are from the South which is maybe why I have always heard it as yīn wèi.

http://en.wiktionary.org/wiki/%E5%9B%A0%E4%B8%BA says:


  因为 (simplified, Pinyin yīnwèi or yīnwéi, traditional 因為)