This is such an old.post but i just had to add. First, this site is amazing. As being a 1st time chicken mother, this site has saved me numerous times from being up sh creek without a paddle, hiben great dos and donts info, helped build my coop, and kept me sane. Second, Im glad i found this post. My chicks are 3 weeks old and have been doing this weird 'tremble' for the past 2 weeks that i was beginning to think was them being frightened, but i noticed they did it as they were falling asleep in my hands. Then my 13 yr old neice states 'i think they r purring!' what a genius this girl is. They don't make.noise just the tremble. Can't cait until they do purr with the noise. Thanks BYC for yet another great lesson.