Here are a few things you should try:

 - Delete or Deactivate all apps that could use audio, especially the app that turns on automatically(Apollo).Then check for the problem again. If the problem is gone, install the deleted apps one by one to see which app is the defaulter. If the problem persists try the next step

 - Use both a earphone and a earphone + microphone auxiliary connector. This could be if your phone is too old (though it is from May 2013) or if the aux connector in the phone is broken.

 - Try using the inbuilt or 3rd party Hardware test app.


 - *RESET*