THIS IS THE STATIC-GATE everyone is talking about over 3g connection. If you record audio in a video or voice note, it will record the crackling/buzzing from 3g. You can show this video to apple store since it is very very hard to reproduce this at the store due to the loud environment. Plus, there may be an environmental reason for the buzzing.
https://discussions.apple.com/message/16681345#16681345
Things test so you know its the same issue.
1. if you are on edge, you won't hear this noise, you may hear the typical GSM buzz though
2. if you are on wifi, and go to google maps, you won't hear it, but if you get a phone call or switch to 3g while on maps you will hear it. try running speedtest with 3g on.
3. turn on airplane mode and you won't hear it
4. listen to all locations on the phone, even at the bottom of the phone at the back and you will still hear the buzz when 3g is loading something.
I have already replaced my first 4S with no change to the 3g buzzing. I don't know what to do at this point. Apple needs to come up with a software fix so that we can't hear this anymore. Maybe by lowering the db from the speakers.
I think the real reason everyone isn't complaining is because it can be intermittent and dependant on where you are. Also you can't hear it with any background noise since it just blends in.