No sound at all

When I play Minecraft, I get absolutely no sound at all. I have confirmed that both Minecraft volume and Windows volume are not muted, and Minecraft is set at full volume in the mixer.
The `latest.log` file shows numerous entries such as: "[21:21:15] [Client thread/WARN]: Unable to play unknown soundEvent: minecraft:gui.button.press", apparently every time it attempts to play a sound.
The log says OpenAL is loaded, and the sound engine is started.
This is a fresh install, I have tried reinstalling, and it works from both the installer and launcher. Each time the launcher runs, it says it is downloading the sounds.