The so called beat frequency is sensed more by the human ear than the airframe.
This whole phenomena is about perceptions of the human ear and while likely associated with something spinning in the innards of the airframe it is very unlikely to be associated with causing any kind of damage to a critical aircraft structure.
I tend to think of the explanation of two disimilar drum heads sitting in the middle of the aisle of a plane. One begins to hum while the other doesn't and then when it stops then its neighbor starts and so on until they both become quiet. Bothersome to the ear but nothing else to be concerned about.