Yeah, Peteski, the metal axles in the metal frame slots is probably a place where some oil is appropriate.
But like I've tried to explain, adding oil there did not change this behavior one bit.
I felt that after I tried that, there was more oil in there than I want, so I cleaned it all up, and brushed/wiped out
that whole area, and inside the gearplate, and the gears, with alcohol to get it as clean as possible.
There is probably still a little oil in there.
I do oil motor bearings, especially if they squeal or the motor seems to be drawing more current than normal.
That's one place where a drop (and only ONE drop!) really is needed.
I suppose it is remotely possible that it is the tender, but the noise most commonly happens when the engine
is over a switch (even though, as I mentioned, it does sometimes happen on curves). Just by being close enough
to it with my head, I can pretty clearly tell that it's coming from the engine, not the tender, and the fact
that it mostly coincides with the engine being on a switch really makes me doubt it's the tender.
I think it's the drivers scraping or dragging over a rail, and the frog would be a good place for that to
happen. As to HOW that could be making such a noise, however, is the mystery.