Are you sure? What about a Bunsen burner. That's just gas but they make a sound. I think the sound is a result of the air around the fire being rapidly heated, expanding and rising. So is it the fire, the flammable substance or the air that's making the sound? None would exist in This state without the other.

I dunno man. I think it would be more accurate if you sorted them by weight. But please use the metric system because obvious reasons.