almost no audio in buster/sid

[Lucio]

I run regular updates of my testing/unstable Debian instance, on my Dell 
Precision M4500 notebook.

A few days ago most applications stopped playing sounds, but not all of 
them. For example Chrome doesn't play sounds, Firefox doesn't, vlc 
doesn't, xine doesn't, while xboard does, audacity does and hydrogen does.

pavucontrol lists no hardware output devices, only a "dummy" software 
output device, but I don't know if this is normal. In the Playback tab 
of pavucontrol I can see the applications names while they're supposed 
to play sounds and I can see digital vu-meters going back and forth. 
They aren't muted, yet the application does not produce any sound.

What should I check?