If you go into spectator mode, and spectate a Enderman you can still hear the audio but right when he starts to teleport you can't hear anything. I also noticed that you aren't Face level with the Enderman, your still 2 blocks tall.

Update: I noticed that once your start spectating you can hear everything, but once the mob your spectating starts moving away from the area you started spectating, you can't hear anything unless the mob goes to back to the area were you started to specate.

Steps to Reproduce:
1. Spawn in a slime of any size.
2. Go into spectate mode and spectate the slime.
3. Wait for the slime to start moving and you'll notice the slimes squishing noise gets quieter and quieter till their is no noise at all from anything.