Coolant always boils into the turbo res after shut down. That is normal. That is how the system works. That is why you dont need a turbo timer. Coolant from the block rises through the turbo and into the res as the motor and turbo cool after shut down. I put a post up long ago that explains this.
But the sounds at start up should not be there and lead me to believe there is still air trapped (possibly in the heater core).
I trust you know what you are doing filling the cooling system and I admit it is an oddity.