Could you determine from which of the speakers (the earpiece or the main speaker) of the phone does the tone or beep come from? Does it sound like a phone key has been pressed, producing a DTMF type of tone?
Thanks. Could you try the following so we can eliminate some probable causes:
1. Try calling but with your headset on (reduce the volume of the phone to around 4 or 5 to prevent possible hearing damage);
2. Try enabling loud speaker when calling.
Let us know if you hear the tone through your headset, loudspeaker, or both.