In construction_drone.lua the volume is set incorrectly.
probability = 1 / (8 * 60),
volume = 0.5, -- does not work when placed here
Should be changed as shown below for each filename.
-- example code
sound =
{
{ filename = path .. "sounds/construction_drone_1.ogg", volume = 0.5},
{ filename = path .. "sounds/construction_drone_2.ogg", volume = 0.5},
...
See official Prototype Docs for this here: https://lua-api.factorio.com/latest/types/WorkingSound.html
