[bedifferent]

is this a broody thing??

[poultrygeist]

It's a contented chicken noise  
..but they might be broody as well of course !

Rob

[Aunt Sally]

Depends when they're doing it.  If they are sat on their nest all fluffed up and it's a shrill growl then they're broody.  But if it's while they are having fun like dust bathing  then is a purr of pleasure.

[SnooziSuzi]

Mine (fully grown and 2-3 years old) have started making cheeping noises when I let them out of the run and into the garden!

It's as if they're saying "oooo!  OOOO!  grasss!!!!  Yum!  Oooo!   yum!"