I don't know if I could find that thread as it was originally about r/c something or another, and then branched into sympathetic harmonics & gearboxs somehow. Anyway, Huber went way, way, really way out on a limb with a long thing about the subject from what I remember. I had to respond to that one as I used to teach the subject a little. I do remember thinking that he had a real attitude about himself when he was expounding upon his knowledge of the subject. He was booted right after that and I never took the time to write my final reply to him about it. It could probably be found with a search of sympathetic resonance, gearbox, ground resonance, critical tailboom dynamic modes, or similar key words. He was smug about what he thought he knew and I just didn't have the patience to try and correct him. With his attitude, he wasn't worth the time or trouble.

I just remembered something: a search for "pylon whirl" may get it.