yay!!! stumbled upon the solution... the YOUTUBE AUDIO Silence mystery solved:VISUALLY below video on Youtube--
Speaker-horn Icon ` ``x`` ` next to the video mark-counter [0:00]
With your (mouse) pointer on the "x"--- you can CLICK, and "x" toggles on and off, but there can STILL be "no audio play"....
When you place the pointer (mouse) on the "X" and CLICK to make the "x" go away, THEN you need to put your pointer on the faint "white vertical skinny beam (line)" that appears, and hold down and "stretch" this towards the right.
This new 'white line' turns into the old and "familiar" "VOLUME CONTROL" .... red horizontal bar.
FURTHER NOTE:
The restored youtube video/AUDIO can act "normally" for a while, then BOOM----- you can lapse back to "no sound" again. The tiny little faint "x" reappears.
>> Hit the faint little "x", and it toggles off....
>> see the faint 'white vertical skinny line' and
>> place your pointer on this line and
>> "stretch it out" to the right [east] again.
You've Got SOUND!! YAY!!!
The clue PixieJane mentioned above (and persistence and luck) helped me solve the riddle--- the audio can 'automatically' turn itself off and on.
================== on 10/8 at 5:36am
MIRAGE FROM HER REPORTING DESK: *click, click*
aw heck!! youtube is STILL shifting its control-stuff around and CHANGING themselves.... It's them, not me! hehe. Well, maybe~~ a little me...but NOT THIS much, hey! *laughing* LMAO
Much shifting around over past 24 hours ... plus the slow downloads were a problem early in the evening 10/7.
Hitting the "x" is NOT the key... it's all in trying to make that volume control appear. Shows up different on different sets of youtubes..... sheesh!!!
I'm gonna figure it out, dammit!!