Oh god, I know exactly the sound you mean.

My parents once drove from Philadelphia to Boston with one Siamese cat and her two Tonkinese children. She herself acclimated reasonably well to the trip, having weathered multiple moves before; her daughter protested and then settled in resentfully for the long haul; her son made that noise all the way to Boston, or at least until he lost his voice somewhere in New England. I really sympathize with my parents now.

[edit] Good icon.