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with an average of
Is it possible that these users are experiencing some form of this [link], considering their mics do work sometimes?
In other words, some app muted the mic, which, as I pointed out in the G+ post, is, shockingly, an operation that sticks even through reboots. Try this app to unmute and see if the mic works again: [link] (toggle it a few times just in case and leave in unmuted mode).