Ok last summer towards the end of it when it was starting to get cooler and i mean not hitting 100 everyday,On the 1st start of the day or when it has had a few hours for the car to cool,it makes a sound as if its a backfire from under the car,sounds like from the passenger just behind the block,but before the cats,its not real loud and only does it one time,then when summer was over it stopped now that the temps are hitting around 75-80 it has started that same thing again.Its seems to idle good but only backfires after it has not been running for a few hours.No check engine light...nothing.Any ideas as to what I should check.80k miles on it,changed plugs about 10k miles ago and the normal tune-up.