I have a Sony Bravia KD-43XE8004 tv and put it on a hd channel. I watched for 10 minutes before muting it and going downstairs for some breakfast.
I came back upstairs after 30 minutes, unmuted it and now I hear sound interference, which sounds a little like an old school alarm going off. I can hear the proper audio in the background. This happens on ALL hd channels. If I change to a non-HD channel its ok. If I put my ps4 on its ok.
I've got the latest firmware installed. I thought it might have been youview but I turned youview off and the sound problem was still there. I went to another hd sony tv in the house, an older tv, and that can hear the hd channels perfectly.
I can't tell what app was updated when. It's frustrating. I'll give it a few days before I put in some complaint to sony. I'm not a fan of these overly technical tv's adding things on we don't want, and then when a problem arises its difficult to diagnose.