Welcome to Android Central! Which Nexus 7 do you have--the 2012 or 2013 version? If it's the 2013 version and you're on Marshmallow, then go to Settings>Apps, tap the Menu button and then Show System, then select Camera, then Permissions, and look for the Microphone permission.
Does the tablet play other sounds without problems, like music, game sounds, etc.? Are you sure your Media volume is turned up? Go to Settings>Sound & Notifications, and make sure the Media volume slider is not turned all the way down.
06-26-2016 10:03 PM