The majority are when the audio momentarily drops though there is one where there's a definite spike. It'd be helpful to see the entire audio waveform showing the audio clips relative to the timeline. That way might show if they occur due to the following possibility.
Might consider putting a slight decibel dip at the ends of all the clips to keep from introducing an immediate sharp transition where they momentarily overlap. It might not be due to the effect applied at all but the way the clips step on each other be it briefly. If the crackles occur where the audio lanes change then that's where I'd concentrate.