Motherboards Lost sound but gained interference

Well, it's either the motherboard or Windows. And I'm very cross either way.

All working fine earlier, playing Mixcloud with no issues (other than that the volume seemed quite low, was having to turn the amp up further to get a decent sound) but now I have no sound at all. Nothing from online sources, nothing from local games. Levels are green and moving in sound mixer, test option gives more noise/interference in a "test-consistent pattern" (therefore I assume something is being sent to the speakers), but no sound related to what is being requested.

I've uninstalled all sound devices in Device Manager and rebooted, I've tested using the headphone port as well as/in isolation from the rear panel jack, I've played music from my phone through the amp and speakers and that was fine and at expected volume for load, so now I'm at a loss.

Either the motherboard sound parts have died (how to test?) or Windows is being stubborn and obtuse.

Grateful for any assistance!

 

Oh well - to close this one out, an overnight shutdown seems to have resolved the issue (even after multiple restarts yesterday). No idea what caused the problem, or how it was effectively remediated - these are the dramas I think I find more frustrating as there is no apparent solution should it happen again. Maybe the hardware is on the way out...