do you have a calibrated board and sensor.
If this is the case, the sensor has been checket here at Libelium and it should work properly, but you'd need to do a couple of things regarding your code:
First of all, please use the API 025 version, where automated gain selection and calibration compensation has been included, and remove the setAudioGain line.
Secondly, turn on the RTC just after turning on the board, in the setup, and before turning on the sensor (it is within this function where the gain is configurated).
Please, try this and let us know.
In case your board was not calibrated (you should have a board, sensor and Waspmote labeled to work together) please contact our sales department fulfilling this form