I recently started having issues with the iPhone buzzing during calls. It seems to have really started with the update to 3.0 software.
I barely hear the buzzing on my end, but the people I speak to tell me they hear it and it is loud and almost unbearable. Location does not matter. I can be sitting 2 feet away from my home stereo speakers and it will randomly buzz, or I can be standing out back 50 feet from my house, surrounded by woods and it will randomly buzz.
I have tried restoring back to factory settings.
I have a 2G iPhone that is long out of warranty and don't know what to do. I can not afford a new iPhone.
I also have a friend that recently started to experience the same thing. His iPhone is Jailbroken, mine is not.
I have Motorola SLVR L7 that had this problem; sounded like GSM buzz on both lines. Pressing "mute" removed the buzzing, which indicated it was the microphone. I replaced the board inside the phone which contained the microphone and the buzzing went away.
During a call, try muting it and see if the buzzing disappears. I know the iPhone isn't an L7, but it's worth a try.