To keep this brief - I'm an idiot. It's all my own fault. Sorry for wasting people's time reading my scribbles.
Now the longer version. I did some extensive tests, playing local music via VLC - OK. Remote server music via VLC and foobar (under wine) - Not OK. Internet music (Firefox, BBC radio streams) - Not OK. Ethernet vs Wi-Fi - no difference. I then looked at my notes for any modifications I might have made in the past, and there it was. I had changed the default pulse-audio bit rate in /etc/pulse/daemon.conf to suit another application using a different output device. My memory being what it is (age...) I had totally forgotten. Reverting to standard fixed the problem. I don't really understand why local music under VLC was OK and other's not, but no matter. The problem has gone away.
To keep this brief - I'm an idiot. It's all my own fault. Sorry for wasting people's time reading my scribbles.
Now the longer version. I did some extensive tests, playing local music via VLC - OK. Remote server music via VLC and foobar (under wine) - Not OK. Internet music (Firefox, BBC radio streams) - Not OK. Ethernet vs Wi-Fi - no difference. I then looked at my notes for any modifications I might have made in the past, and there it was. I had changed the default pulse-audio bit rate in /etc/pulse/ daemon. conf to suit another application using a different output device. My memory being what it is (age...) I had totally forgotten. Reverting to standard fixed the problem. I don't really understand why local music under VLC was OK and other's not, but no matter. The problem has gone away.
Now I shall go away and hide....