Ah! The classic 'cut-cut-cut-cut-cut-cut-cutAWK!' repeated ad nauseum! Yes, roosters cluck like that too...usually everyone nearby will join in when somebody sounds off like that, really noisy! Usually set off by someone laying an egg, but you're right...I've seen my chief rooster start one of these cluckfests all by himself when he was outside in his run and I still have no real idea why he does it or what sets him off. Maybe it's just about unifying the flock at times? Everyone yells together like a bunch of rowdy fans at a football match to get that community spirit flowing?