Why does my phone beep during phone calls?

[AC Question]

I have a ZTE Z930L and 3 days ago my phone started beeping during phone calls. It is not another call or notifications either.

 

[B. Diddy]

Welcome to Android Central! Does it beep around every minute? It might be a "minute minder" feature, to remind you of how much time you're spending on a call. Open the Phone app, tap Menu>Settings, and look around for a minute minder option.