DIAGNOSIS This is a known bandwidth/interference issue with the wireless connection between the Apple TV 4K (3rd gen) and HomePods when streaming high-bitrate Dolby Atmos content. The wireless audio stream is competing with your Wi-Fi.
FIX Ensure both the Apple TV and the HomePods are on the same, stable 5GHz Wi-Fi network. The best fix is to connect the Apple TV to your router via Ethernet (using a USB-C to Ethernet adapter). This takes all the video/audio streaming load off the Wi-Fi, leaving a cleaner path for the wireless audio to the HomePods.
IF THAT DIDN'T WORK Try changing your router's 5GHz channel width. Log into your router's settings and if the 5GHz band is set to a wide channel (like 80MHz or 160MHz), try narrowing it to 40MHz. This can be more stable for time-sensitive audio streaming, even if it reduces maximum speed.
HEADS UP This problem is most pronounced with high-quality sources like Apple TV+ movies, 4K Blu-ray rips, or Disney+ IMAX Enhanced titles. If you're only having issues with one app (like Netflix), check that your audio format in the Apple TV settings is set to 'Auto' and that the specific show/movie actually supports Atmos—some don't, and the switching can cause a hiccup.