Hello.

Playing audio (be it with or without video) on my Raspberry Pi 4 using VLC, mplayer and mocp, at all volumes, produces a slight crackling. The audio and video was downloaded from Youtube using youtube-dl.

The only other way of playing sound that I have tried is through Firefox (Youtube and some online classes), which doesn't crackle at all. On Youtube, however, some videos play sound and some don't. Also the videos that do play sound are muted unless they are at 100% volume (this happens in both Youtube and online classes). I don't know if this is related to the crackling thing.

I am using raspbian lite, bluetooth headphones, pulseaudio.

The crackling sounds like sample 3 from this video:
https://www.youtube.com/watch?v=LQKylPGnjeY

It wasn't very helpful to link to a vinyl stylus! You should have linked one of your problem videos.

Sound is fine in the Pi over hdmi. I might expect a slight electrical noise, because the parts on the Pi should really be spread out better - I don't like the way the pcb is built.Verify your sound over wires at volume. If it works, which I expect it to, then it's the bluetooth. Does it happen on vimeo videos?