Which year/model is your ATV 4K? 2018 or 2021? I'd try contacting Apple Support, especially if it's the newer one.
I've had some audio issues recently with my 2021 model but it's occasional dropouts, not something continuous. I did end up contacting Apple Support and having a long conversation with a guy there. I actually had 2 problems to discuss, the primary one being that every 2-5 days it would not be able to start playing video until a reboot. That seems to have been solved by assigning the ATV a static IP address. That didn't affect the audio dropouts though, and neither did switching to a certified 48Gbps cable. (He rabbit holed for 45 minutes on HDMI issues.)