Give this one a chance! It sounds odd, but I find that pouring cavity puffs into a glass bowl produces multiple pleasing sounds simultaneously. Just give it a listen. Several people commented on the sound of the cavity puffs being poured into the bowl in my "Joyce" roleplay earlier today, so here you have it - a whole video of just that! :)
To listen while using other apps, switch the player to Picture-in-Picture (PiP) during playback — it keeps playing in a small floating window (the screen stays on).
To listen with the screen fully off, in-browser playback stops by YouTube's design. Open the video in the YouTube app to keep listening where background playback is supported (e.g. with YouTube Premium).
Open in YouTube app