To add to your point 1 - no particular mental focus also requires no audio input. It's so easy to fall into the habit of constantly having a podcast or an audiobook on.
Actually, audio and especially music can make it easier to go into a diffuse state. The trick is to make sure it's music without lyrics, or the volume is low enough you're not listening to the content of the talking.
Or, it's a song you've listened to a hundred times already and know the lyrics and the tempo by heart. At least, it works for me.
I can't confirm that, since as of late I've been getting great results with this:
Of all places I thought I'd see that channel recommended, HN is close to last on the list. That guy puts up some really great stuff.
I originally found this channel searching for "Saturn noises". And Saturn noises I got.
Not sure how to interpret the "no audio input" part; for years, I've been able to get into this kind of flow simply by starting a minimalist, repetitive tune on a keyboard and let that run for an hour or longer. My most effective place for this is early morning events where the secret sauce is to avoid opening your eyes until the idea that is emerging is fully baked in your memory.
What’s wrong with music?
Nothing inherently wrong, but if your mind is thinking about the lyrics it might be hard to "wander". Of course varies from person to person