I am having the EXACT SAME PROBLEM, its driving me crazy. I have the 7+, this happened to me literally from one moment to the other, i took it to the apple store: the genius bar and they could not figure it out. They said to swap the phone it would be $349, due to being out of warranty. Basically told me i need a new phone. UGH, Were you able to fix this? Im thinking i will have to replace the microphone??