If I had a farm I would almost bet the whole thing the noise is a pop inside the exhaust from winding down like nm9stheham mentioned.
Fresh air pulled in around a leak gives unburned fuel the oxygen to ignite.
I knew whenever my header collector bolts came loose on my Duster because it would start popping out the exhaust on decel, normally it never does that. I finally redid the down pipes because the first set were dragging and hitting everything.
