I had that problem one week ago, i hear a sound when i make calls or during a entrance call, and the only solution was to return the iphone to carrier. I tryed restoring, upgrading, everything. The problem is Hardware related, at first worked fine, but after 4 days it got funky.
They sent a refurbish one, the solution was solved, but i got a worst one ( WIFI, GPS and bluetooth *****, weak signal on wifi, gps inaccurate).
So i do recommend to get to your carrier and get a replacement.