Well, one day Frank Van Alstine called me and he needed some changes done to one of the products. Turns out, the "on" LEDs was "F"ing up the transformer and causing DC offset (as I recall the problem) and causing hum.
Uh, wait, what? What? WHAT?
Exactly how can an LED affect a power transformer?
An LED draws a few milliAmps! So unless the LED had failed as a
dead short no physical mechanism exists for the power supply to be affected. It just doesn't make any sense from any physical perspective.
Neither could an LED cause "DC offset" which is an mean displacement above zero. So the LED somehow lifted the baseline? Wait, what? How would that get into the rest of the circuit? This is a solid-state light bulb powered by some low-voltage winding.
Furthermore, "hum" is a noise issue. Hum typically means mains frequency or a low harmonic, such as 60 Hz or 120 Hz. A diode does not make noise like that. LEDs, in point of fact, have such low noise properties that audiophiles actually build circuits using LEDs as voltage regulators, as a Zener would be noisier. The carbon-composite resistors used for the rest of the gear will be many orders of magnitude noisier.
But, again, the LED in question is not used to set bias or for voltage regulation. It is to illuminate a dial or meter. So it CANNOT affect bias.
Weren't you an electrical engineer at AVA? How about some technical details here. Because this anecdote surely is 52 cards short of a full deck.
Another time, I had an issue with one of my preamps. It was a strange noise in one of the channels. After a lengthy time on the bench, it was determined that it was a RESISTOR causing the noise. Frank had never, ever in his entire career come across a resistor problem like this before. Tales from the crypt.
Ummm, unless that "RESISTOR" involves an LED used for illumination that's a red herring. We're not discussing resistors, we are discussing LEDs used for illumination.
Resistor noise, from carbon composite or carbon film, is well known and well understood. I have many times discussed the issue of why carbon-composite is a poor resistor technology. I've quoted Hafler's problems at Dynaco because the cracked-carbon resistors were noisy and even the legendary Stu Hegeman couldn't find it.
But, again, what exactly does this have to do with LEDs? Oh, right, nothing. Distraction.
Randomly changing components may cause correlated effects, as poor solder joints can be flexed during debugging. That may cause a problem to arise or vanish, but it does not mean that an illumination device is the cause.
It makes absolutely no sense that a glowing LED used to illuminate a meter or dial could cause any noise and thus requires a switch or other disconnection device.
I'll leave you with an observation from M. Le Comte Laplace (which I pulled from my quotes archive):
"De ce qui précède, nous devons généralement conclure que plus un fait est extraordinaire, plus il a besoin d’être appuyé de fortes preuves. Car ceux qui l’attestent, pouvant ou tromper, ou avoir été trompés, ces deux causes sont d’autant plus probables, que la réalité du fait l’est moins en elle-même. C’est ce que l’on verra particulièrement, lorsque nous parlerons de la probabilité des témoignages."
M. Le Comte Laplace, Pierre-Simon:
Essai Philosophique Sur Les Probabilités (Sixième Édition) (1840)
In case your French is worse than mine, I roughly translate that (the Google translation is execrable) as:
From the foregoing, we must generally conclude that the more extraordinary a fact is, the more it requires support by strong proofs. Because the attestor possibly is deceitful, or had been deceived, these two causes being all the more probable, since the reality of the fact will itself be lesser. This is what is particularly seen when one discusses the testimony's probability.
TL/DR: extraordinary facts require strong supporting proofs. The burden has not been met in this case and furthermore, I'd argue, cannot be met.