Diagnosis
The TV's Sound Output is set incorrectly for HDMI. It's trying to send audio back out.
How to Fix It
Press the Settings button on the remote. Go to All Settings > Sound > Advanced Settings > Sound Out. Change it from 'HDMI ARC' or 'External Speaker' to 'TV Speaker'.
If That Didn't Work
The HDMI port may be set to PCM only. Go to All Settings > General > Devices > HDMI Settings > HDMI Deep Color. Turn it OFF for the problem port. Also check 'Digital Sound Out' is set to PCM.
Heads Up
If using a soundbar on HDMI 2 (ARC), you must set Sound Out to 'HDMI ARC'. For other HDMI ports, use 'TV Speaker'.