After a 4-5 hour highway drive this summer, I heard a strange noise while running and parked at home. It was a whistle more than a whine. It was somewhere out back, and I suspect the fuel pump. The noise left when the vehicle cooled off. It happened again today in 30 degree weather. I usually have seen pumps work or not. Am I missing anything else back there that could make whine/whistles outside the rear of the car?