No sounds in this snapshot, 'Missing sound for event', (Silent mode)

When starting snapshot 17w43a, there is no sound. Version 1.12.2 (and other versions) work fine. The launcher logs that files are missing, as follows;

Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release
[01:52:20] [Client thread/INFO]: Setting user: <<<NAME REMOVED>>>
[01:52:22] [Client thread/WARN]: Skipping bad option: lastServer:
[01:52:22] [Client thread/INFO]: LWJGL Version: 3.1.2 build 29
[01:52:23] [Client thread/INFO]: Reloading ResourceManager: Default
[01:52:23] [Client thread/WARN]: Missing sound for event: minecraft:ambient.cave
[01:52:23] [Client thread/WARN]: Missing sound for event: minecraft:block.anvil.break
[01:52:23] [Client thread/WARN]: Missing sound for event: minecraft:block.anvil.destroy
[01:52:23] [Client thread/WARN]: Missing sound for event: minecraft:block.anvil.fall

(snipping 544 lines, showing the same message for - presumably - all sounds)

[01:52:23] [Client thread/WARN]: Missing sound for event: minecraft:weather.rain.above
[01:52:23] [Sound Library Loader/INFO]: Starting up SoundSystem...
[01:52:24] [Thread-2/INFO]: Initializing No Sound
[01:52:24] [Thread-2/INFO]: (Silent Mode)
[01:52:24] [Thread-2/INFO]: OpenAL initialized.
[01:52:24] [Sound Library Loader/INFO]: Sound engine started
[01:52:26] [Client thread/INFO]: Created: 1024x512 textures-atlas
[01:52:27] [Client thread/INFO]: Narrator library successfully loaded
[01:52:27] [Client thread/ERROR]: Realms module missing
[01:52:33] [Client thread/INFO]: Stopping!
[01:52:33] [Client thread/INFO]: SoundSystem shutting down...
[01:52:34] [Client thread/WARN]: Author: Paul Lamb, www.paulscode.com
AL lib: (EE) alc_cleanup: 1 device not closed

I have tried completely reinstalling, with the same effect. There are no other errors; all files seem to have downloaded correctly - I can manually browse/locate the sound files and play them.

Narrator works as normal, making sound. The /playsound says it plays sounds, but does not make sounds. F3 and T has no effect.

I also tried the newer launcher (from http://launcher.mojang.com/staging/) and got exactly the same results.

I removed everything (deleted .minecraft), reinstalled and rebooted between these attempts. Other versions work (1.12.2, 1.11.2, 1.10.2, 1.9.4), whether installed before or after this one. I tried (separately, fresh install again) adding a resourcepack which contained sounds, which had no effect.