I've had the issue too every now and then on Mageia 6 x86_64, using PulseAudio 10.0.0. It's usually only for a few seconds and then things get back to a working state. IIRC I had a similar issue recently with another Godot game, but it never happened in past years, so I suspect a system-specific issue, maybe due to a kernel update or similar. I'll make an upstream bug report if I found out how to reproduce it reliably, though it might be fixed in Godot 3.0 already.