What and how to fix the "Beep" sound during calls?

[Acer Gallant Duo]

During a phone call on my Acer E350 Liquid Gallant Duo, it keeps making the "Beep" sound every now and then. It was like a "call waiting" but there weren't any one calling. I checked "sound setting" and nothing there to explain the "Beep" noise. Does anyone has an idea of what is is, why it is "Beeping" and how I may tackle the problem?

Thanks a bunch!

 

[Doit2it]

It sounds like the minute minder that beeps every minute to remind you how long you've been on a call. Not sure about your specific phone. On most phones open the Dialer/Phone app (not Contacts) / Menu key / Settings / Call alert / Call status tones / uncheck Minute minder.