Hope this is simple, but I did extensive fruitless search including web, forum,
manual, how to, looking in the program directory for audio files to delete,
preference .ini, etc.

How to delete, turn off, destroy, forever banish the obnoxious and alarming
sound that goes off when a download is complete? 

I have all sounds turned off in everything on my computer and usually have
mute on to avoid exactly these sorts of unwanted annoyances, but sometimes
forget - as just a while ago when the OBNOXIOUS sound blasted out at high
volume in this otherwise quiet university lab!

win version, by the way.
It's a lot more sensible to just watch the program and see myself what it's
doing, don't need alarms!