Solved. It is the dock connector with the antennes!! Same problem here. Just started at a certain point make noise during call. Replaced speaker, no success. Cleaned earphone jack, no success. I finally opened the iPhone and took the dock connector out. Inspecting the dock connector, I noticed that there was dirt around the connector. Actually there was sand (silicium, quartz) sticking between the black housing and (what I think are)antennes. I guess the sand comes from keeping the iPhone unprotected in your pockets. Silicium and quartz are electric sensitive. I cleaned it away with a brush and small screwdriver.That really helped. No noise during calls anymore. My guess is that some sand grain punctured an antenne or made a short circuit to the housing of the connector. So, try cleaning dock connector around the connector housing.