Why does my iPhone bleep at me when I make a call?

I’ve got a few email accounts that don’t support Push. On the Settings->Mail->Fetch New Data screen, you can choose whether to fetch new data every 15 minutes, 30 minutes, Hourly, or Manually. An uncharacteristically long paragraph of text explains that for better battery life, fetch less often, so I had it set to Manually. Almost every time I make or take a call, the phone dings at me as soon as I hold it up to my ear, and even though I know it’s telling me it has new email, it’s still surprising and disruptive, because I’m not expecting it to do that.