Why Is It?

Why is it that kids can be SO ear piercing at home, outside, in a store (LOL), etc. but you get them in a van and they whisper questions to you? Don't get me wrong. They are not always quiet in the van. They can be loud in there too but not for long because we don't allow loud noises in the van. (too distracting for the driver) What gets me is that nearly every time they try to ask us something in the van they whisper in a tiny tiny voice. We say, "Speak louder. We can't hear you." They up the volume to just under what my ears can hear. It's so weird.