I had an issue with my Sony Bravia where the volume and mute buttons on the remote and the TV would not work after the latest firmware update.
I tried tinkering with the settings, all of the regular fixes in here and on Sony's support pages & factory reset but they didn't work. I eventually fixed it by taking the USB for my PS4 charger cable out of the TV usb port and restarting the TV.
I guess because the PS4 controller has a speaker built in, the TV was thinking this was some audio out device. Hope this helps anyone with the same issue.