Any AF mic. can have this crackle problem.
I would assume that the KM84 is a lot older than the KM120 ???

An AF mic. attracts dust and contaminants to the diaphragm by electrostatic action - these contaminants can absorb moisture and cause the crackling.

If the 120 is much newer is would be much cleaner and will last longer before the crackling starts.

I'm not sure how easy it is to clean the diaphragm of the KM84, but if Neumann can do this for you it should improve things greatly.

Maybe Martin or Uwe can answer this.

John Willett
Circle Sound Services