How to activate the loot goblin vampire?

So there is a yellow vampire thant appears to spawn during either Wave 3 or 4 of nightmare that has a ton of HP and drops a ton of loot.

My Question is: How do you consistently spawn him?

I know most think he is random BUT...

There appears at the start of either NM Wave 3 or 4 gold fire flashes that move around the map. There is also what appears to be a yellow shield icon that will hover above your reticle that seems to indicate that he is nearby. When ever I have triggered him he appears near the last place I saw a flash. So is there any way to consistently trigger him to increase the drop rate?