As far as vibrations during ELT or transverse flow are concerned- there will always be vibrations present whenever there are differences in drag across the span of the blade which are moving inboard/outboard as the rotor is turning. Anything other than a calm wind hover will produce vibrations in the rotor disc.
To ask a student to try to distinguish an ETL vibration from transverse flow vibration seems a bit ridiculous to me- you might be kidding yourself if you really believe that these vibrations occur separately and only at different times.... RW aerodynamics are far too dynamic to deconstruct them and then try to distill some type of "rule" that will apply in all instances.
How the rotor disc behaves, however, gives the pilot an indication of which, of many, phenomena he is experiencing. And he is always experiencing more than one at any given time!
And what about Hooks Joint Effect?
