I have a similar issue but it resolves when I unplugged my webcam, which has a built-in Mic. I still see my Mic icon flash though the complaints seem to stop. Whenever it is plugged in though other people get echo and nothing I say transmits. I either have to forgo hoping to talk to my team or use an external program like Skype or Razer comms and just annoy people who haven't muted or gotten a chance to mute me since I can't mute myself and others can't mute me midgame.
