Not in any particular order.

1. They are testing their communications links by transmitting simulated biomedical telemetry and voice communications. This would be a very sensible thing to do, especially if they're almost ready for a human crew.

2. The voice picked up could be similar to "Bitching Betty", the alarm system carried on many of our military planes to alert the pilot to a problem. Studies proved the pilots paid more attention to a female voice than to a male voice. No doubt their wives question the results of this study.

3. There could be someone on-board. If that's the case, we'll probably know pretty soon.