I posted on the forum back in June/July about this. I called Apple and have a case with them now, and plan on calling them back tomorrow.
The problem is only sound, and only occurs when watching shows in dolby atmos. This happened to be after I got it new this year, so it's always been there. I received it in the mail directly from Apple on day 1 of release because I pre-ordered it.
The sound will sometimes drop out on Netflix, but the DolbyVision is fine. It will eventually come back on in about 10 seconds, or if I pause the show and then play it is fine after that. It's random, and occurs at any time. Sometimes I can watch a whole movie and it never happens, other times it can happen 3x in a 45 minute show. If I rewind over where the sound error occurred, and then play it again; it plays fine and the error doesn't happen.
Sometimes the sound will make a popping sound on random speakers and then fade away, lasting just 5 seconds or so. This happens on Apple tv + shows too. So it's not just Netflix. Apple tv+ hadn't had the sound totally cut out and mute like Netflix, but it makes the popping sounds on speakers.
I'm using the apple tv connected by a wireworld ultraviolet hdmi cable to my Marantz sr8012 11.2 receiver. I'm able to play atmos just fine through my 4k Panasonic player and also through my cheap Amazon Firestick 4k. So it's not a hardware problem with the receiver, and I've never had a problem with the wireworld hdmi cables. It's a high quality cable.
Wondering if anyone else is having this problem. When I called Apple, in June, they told me they had other reports of problems already. At that point it had only been out for a month or so. Online I've found several threads with similar problems.
This page shows that the problem was on the last gen too. So the problem has followed along onto the new one.
My Apple tv is hardwired with ethernet and gets around 500 mbps, so no wifi to worry about. A member on here had me check my connection quality and it tested very good. So it's not my internet connection.
Seems to be some software issue, unless my apple tv box is a lemon. I may see about sending it in for a new one, since it's well within warranty.
I went a month or so without watching shows with Atmos, so I kinda forgot about it. Now I'm watching more and the problem is still there. There have been numerous software patches since June ,but none took care of this .The problem is in both Apple tv+ and Netflix. I've never heard the problem on HBO Max, but haven't watched much on Atmos there.
Thought I'd throw this up and see if anyone else has had this and if anyone has an idea about what's going on.