2007 Toyota Tacoma backfire after stopping

My 2007 Tacoma just started making what I believe is a backfire sound when coming to a complete stop after driving it at highway speed. I think it's coming from engine compartment rather than exhaust but hard to tell. It does not hesitate when accelerating or display any other signs of trouble. It has about 35000 miles on it and is a v-6. Replaced engine air filter about 10000 miles ago. Checked it and it is still clean. Original spark plugs still in it. Nothing but routine maintenance ever done to it.

Any ideas?