Have a check in the device manager properties for the sound card to see if it shows ‘Roll Back Driver’. If the culprit is a new sound driver coming through Windows update, this button will let you go back to the previous driver:
If this doesn’t work or the button is greyed out, I suggest uninstalling the last updates one by one until the sound returns to normal, e.g. any updates shown as released in June or July 2017. If you identify the update (i.e. sound returns to normal after uninstalling a particular update), you can mention the update KB # here.