David, I don't know why they are bothered by it, they just are. They post threads looking for answers why. So I tell them why. If they can live with it, fine. If it doesn't happen to their table, fine. I don't want people to have problems with their analog rigs. If they are happy, they feel better about their music.
As far as saying that it doesn't make an audible difference, I wouldn't be totally sure of that. Just because the hum is reduced below audibility when signal is running, does not mean that it is not affecting the cartridge's magnetic field.
My opinion is that if there is enough hum field strength to make an audible hum, then it is strong enough to influence the magnetic performance of the cartridge, whether the influence manifests itself as hum, or not, while playing.
My point is that even though many people like Grado cartridges, and find them musical, there are other cartridges that are also musical, that do not behave this way on Rega TTs. So I simply conclude that to avoid potential problems of this nature, use a different cartridge on Regas. I really don't think that this is a radical point of view. To me it seems to make alot of sense.
I understand that you have this combo, and are not experiencing this problem, and that is good. I also understand that you may be sensitive to statements like the one I made, because it goes contrary to your selection. But I did not make the statement to irritate you. And I specifically said it did not happen in all cases. But it is quite common.
As far as people not wanting hum, but accepting pops and ticks, perhaps they feel that hum is an avoidable circumstance, and would rather do without it. I know I feel that way.
And also, if I started a thread, as a new TT user, and asked a question about using a Grado with a P3, and everybody said it was fine, and I got a hum problem, I would be wondering what was wrong. Then when I found out that is was a fairly common problem, I would be wondering why nobody told me about it when I asked about this combo. Doesn't this make sense to you? Am I wrong to tell them?
Anyway the subject is closed as far as I am concerned.
Enjoy the music.