There was a HUGE difference in noise/quietness having the "correct" end towards ground. MUCH much more pronounced then doing the same experiment with Orange Drop PS caps of the same value. Dramatic difference.
Same value OD PS cap does have a quiet end. But the noise difference on the OD PS caps was no where near the amount of dramatic difference of the Musicaps. ,,,,,, the dramatic difference between quiet and noise was evident on all 3 caps. You can't miss the difference on the Musicap.
What I can say conclusively is that the values I tried on the Musicaps gave a very easily discerned transparent difference between the ends.
Now wait a dog gone minute now,

Som'thin screwy is going on here.
When this 1st started, on testing for the outside foil, I found, to my ear any way, that the
SMALLER the caps value, the
HARDER it was for
me to hear a noise difference.
BUT, you and Gezzer found the opposite, the
LARGER the value of the cap, the
HARDER it was to hear a difference.
So,
at this point, my conclusion is : There
MUST be something
different in the way you (and Gezzer) are testing caps for the outside foil lead than I am?
Because, ..... I'm getting the opposite results.
And, out of the caps I've been able to test for outside foil, in my test rig, I found that the Musicap was the
LOWEST in difference between outside foil and inside foil lead.
PLUS the Musicap were
WAY lower in noise, from outside/inside, of any of the other caps I tried/tested.
Of all the caps I have tested;
1st; I measured them for capacitance value, no big deal, just to see if their close.
2nd; I tested and marked them for 'outside foil'. (My test's, only 2 caps, showed what you got on the Musicaps, white lead is the outside foil lead.)