I believe Master Volume should adjust the level of all sounds in the game, but sound does not stop when Master Volume is at lowest, there is some kind of effect but it is not the right one, it sounds more like an overdrive when you get a signal over the maximum value.
Sorry if this bug is already known but I tried to find a report about it and I couldn't.
Also it would be nice if there was a "Stop Sound of Pause" feature, everytime I pause the game and take it to the background the sound doesn't stop so I have to go to options and lower each and every volume(since master is not working as stated before)