I've concluded that the crackling sound was just air bubbles and possibly moisture being purged. All is good. However I am also noticing a slight expansion of the cap on the bottom of the sliding yoke. Not sure how bad that is.
When I apply grease to my sliding yoke and U-joints on my 74 Dodge power wagon I hear a poppling sound. I don't know when the last time this vehicle was regreased. The sound is kind of like popping a tiny sheet of bubble wrap. I am hoping this is just the old grease being pushed out of old muddy...