(In reply to comment #20)

> I have tried disabling cpufreq on_demand and also forcing dpm auto/low/high,
> but there is no difference - I need load to make it work.

Been playing more - it seems to be CPU load that I need not GPU.

I can reproduce the issue playing audio without X started from fbcon.

make -j5 &>/dev/null on mesa from another fbcon will make the sound OK.

While I've got rid of cpufreq on_demand I haven't yet managed to stop
acpi_cpufreq loading, though of course it may be innocent - no issues with the
same setup with my 4890.