My least favorite question, but almost invariably the opener- "So...tell me a little bit about yourself."
Beyond that, pretty much all my FM interviews were very conversational. In my experience, most people are mostly trying to figure out how well you would fit in with their program and if they want to work with you for the next 3 years. Some interviewers asked me about stuff on my app or in my PS that they found interesting...either that was an area of common interest for us, or they knew the people I had worked with, or something like that.
Also, be prepared that you will likely be given the opportunity to ask *them* questions. At some of my FM interviews I found that took up at least half of the interview time.