I've just upgraded from a gen1 chromecast to the 4K Google TV device.
When casting audio from my phone to the decive I get audio drop outs around every 30seconds thar last for a fraction of a second.
I have the gen1 chromecast connected to another TV and don't have the drop outs, I also have a nest mini and a nest hub. None of these devices suffer. Although I did have the same problem with the nest hub for a while but this went away after an update.
On the Chromecast Google TV I been to the settings and changed all the audio options but still the same problem. The device is fine when playing from built in apps, it's only when casting from my phone. (Adndroid Samsung S10)
Thanks for reaching out and for being a step ahead of us. Please try to cast audio from a different mobile device. Rebooting your Chromecast with Google TV (4K) and plugging it on a different HDMI port on your TV might also help.