I’ve got the same thing going on (or very similar anyways). Never had any other HDMI issues, but whenever Bazzite makes any sound (whether in gaming mode or desktop mode) I hear a humming static sound that lasts until about 1.5 seconds after the sound ends. Then it ends with a soft pop like something turned off. Out of curiosity are you using an optical audio output from the device you’re running HDMI to?
For me, my stereo set was just turned up super loud. Maxed the PCs volume and turned down my stereo and it evened out for me. I’m sure someone more knowledgeable about audio could explain. I suspect it’s a gain vs actual volume thing.
Haven’t noticed any significant audio issues since.