One other piece of advice [that I gleaned from reading a thread on this forum].
When answering any of the questions "why MD/PhD", "why not phd only", and "why not MD only", it is
very important to be clear and concise in your answer. Don't go into your life's story for why you're choosing this path. In fact, I recommend you only briefly discuss the events leading to your application to MD/PhD. Much more important is answering the question of what you will
do with this degree. How will getting a dual degree fit into your vision of the future?
The same is true when you're asked about your research--be short and clear. In 1-3 minutes, you can explain your reseach like a publication. Explain the background, summarize the methods used, and discuss the results and conclusions. Emphasize your role in the process. Let the interviewers probe you about your research, and be prepared to offer details; but don't delve into unnecessary detail voluntarily.
I'm also going to repeat some advice from above. DONT STRESS OUT. DONT WORRY. I know, it's nearly impossible to comply with this advice. But in all seriousness, chilling out in an interview just might be the most effective way of doing well. I dont know why this is, and I certainly can't tell you
how to calm yourself before that first interview. I can only say that you will do a better job of being yourself if you aren't flippin' out inside your head during that interview.
Lastly, I'm also majoring in an unusual field for an MD/PhD applicant. Maybe not quite as unusual as yourself. In any case, this is a strength. Just be prepared to talk about that, because nearly every interviewer is going to say "wow! that's very exciting.. now how did you get interested in an MD/PhD as a music major?" Remember to follow the guidance above--be short and to the point in your response.
Good luck to you!