Help can you hear me now? microphone shuts off during call

[RebL]

Sporadically, in the middle of a call my mike shuts off, so I can still hear the other person, but they can't hear me. The mute button is not lit, and when I've tried to turn mute on and off, the problem persists: I can hear the other person saying, "hello? are you still there?" When I call back, the problem is gone. Happens on both incoming and outgoing calls, full battery, random # of bars. The service rep said it was from too many apps running and not having ATK. Well, now I use ATK, I've still only downloaded six apps anyway (and this happened when all I had added was Google Maps), and it's still happening

Help me! No wait, you can't hear me...