Started playing MW3 with a friend. I noted that his voice volume seemed lower than usual, so I maxed the volume on my headset. After about 5 minutes, his voice disappeared altogether. I could see on the screen that he was talking, but I could not hear him. I quit playing, turned off the xbox, and came back after 20 minutes. Same issue; others could hear me fine but I could not hear them through headset. I changed setting to TV and I could hear them through the TV. Switched back to headset and got nada. I bought a new headset thinking it was the issue; no change. Tried different controllers (with either headset); no change.
This occurred while I was in-game so it isn't an issue of me accidentally changing some setting. NAT is open.