Determining/stopping random phantom notifications during calls
On some Samsungs, they have a feature called Minute Minder. It will notify you around every minute of your phone call (it is usually 5-10 seconds before the actually minute mark). For people who don't have unlimited minutes, this allows them to easily know how many minutes have passed.

For the original Galaxy S, the setting is located under

Settings -&gt; Call Settings -&gt; All Calls -&gt; Call Status Tones -&gt; Minute Minder

I think with the Galaxy S 4 it's been moved to

Settings -&gt; My Device -&gt; Call -&gt; Call Alerts -&gt; Minute Minder

I'm not positive if this is the cause, but it sounds probable.