tonal

17:31 Feb 3, 2019 

This is a general term, not really specifically to do with lifts; it is used a lot in both acoustics and also vibration study.
'Tonal' means that the sound or vibration tends to have one or more prominent frequencies — a hum, whine, squeal, etc. Of course, vibration will probably be at sub-audio frequencies — but the same principle applies. In acoustic terms, a noise that is tonal ill tend to be more irritating / stand out more from the background than one that is more broadband or frequency-diffuse.
Thus conversely, 'not strongly tonal' means that the sound / vibration does not have a strong component at any particular frequency(ies).
When somethng IS tonal, it usually makes it easier to analyse and diagnose the source of the problem!
Do note, however, that 'not strongly tonal' has nothing whatever to do with the actual amplitude of the vibrations: whether they are weak or strong! It is all about their character.