KNOCK MORE THAN A TICK sound !

[SV DADIDOC]

This came on right after an oil change at my GMC dealership ( but no connection).  As I let up on the gas pedal I can hear a light " knock or click" sound as if something is disengaging when de-accelerating,  where  I release torque completely.  Then, when I apply the gas, and torque is lightly reapplied, I then get this LOUD knocking sound until it shifts into gear.  If I apply the gas fast, I will pass through and get into gear and not hear the sound.  Again, when I lightly apply gas and torque, it will  make this sound .  I am looking for a sure thing diagnosis from a technician who can recognize this nd tell me what needs to be replaced. Terrified that it " could be" this , or that, or this other thing and my bill grows quickly !   I have heard the ticking sound from  flex plate,  understand a shudder from a failing torque converter, but this one puzzles me. 

 

Here is a youtube clip with the noise.