I also guess it is random audit. I have heard that when u work for chip indrustry (mostly on R&D).. there are higher chances that u will be picked for audit... as they want to do extensive background search to make sure that information will not go out of the country. I am also thinking u were picked for audit for same reason.. working in R&D in checmical field.

Chill, everything will be fine for you.

My suggestion, ask your manager to contact US Embassy mentioning that u r working for him and you are being missed becuase of this extended vacation and can contact if they have any question, I bet they will expidite whole process.