Thank you gentlemen,
It was indeed the air pump engaging but I have since disconnected it with no change in the symptoms(other than the fact that the engaging sound has ceased)
I did ask my mechanic and he said it was not an EGR issue but I'm not sure if he meant there was not one involved or it was functioning properly.
He seems to feel it is electrical in nature. It is now occuring more often and now stalls at about every third stop.