my iphone's microphone is not working. what happens is people cannot hear me but i can hear them. ive used the voice memo thing to test the mic. it sometimes works for about 20 seconds then my voice becomes fizzled and muffled. I thought it could be a bad microphone so i had it replaced, but that didnt fix the problem. could it be the charger port or the logic board or the battery. I am so frustrated any help would be nice.