Weird noise from external harddrive.

[Magic Wonder425]

So I was sitting browsing websites and all of a sudden my external harddrive starts to make a humming noise. Now it's usually quiet and this is the first time I've heard it. I let it run for a few minutes then disconnected it to be safe.

I assume it's a result of being tipped over by my sister. I'm not sure what to do about this, but it's a My Book from Western Digital, I can't really open it up since I don't see any way to do so. Does anyone know what the problem could be or what I should do?