Thank you, there should be one sound for digging each type of terrain.
The issue was my implementation of the tile map revealed that the built in gameobjects was not stable. What I learned from this is to create a separate data structure since runtime SO's can be unpredictable. I believe what happened is the rule tile changed and the game object changed. The sound cached found on the gameobject, but for some reason it would become null. Since I handled sound last I didn't have the time to figure out what exactly the ruletiles were doing with the original game object when they changed and just shifted the responsibility to the manager class. (Some sound was better than none).
This was very fun to learn from. There were intially I believe 6 different sounds for ground breaking, I had time to implement two of them, but our composer did a hell of a job on them, they were on freakn point. Wish I could have gotten the rest in.