Yippee, I have finally found a way to get rid of the squares!
And, it was my gut instinct that was correct. A photographic memory isn't that bad at all!!!
The solution, for me anyway, was of course, IE9. I have deleted it with no squares whatsoever, whilst playing audio. (Before, the squares were only disappeared when no audio was playing, and the mixer was opened immediately upon bootup). Now I can open the volume mixer whilst playing audio and have no problems.
I don't think that an advert on television will make me go back to IE9, because of the problems caused. (But anyway I use chrome so IE is not used anyway!)