My ferret cry's when he sleeps?

hello i have 2 ferret's a girl named Snow that is 5 months and a boy named Taz that is 9 months.Taz has been crying a little when he is asleep it make me sad so i give him love and play with him but it makes me more sad not knowing why he cry's sometimes i wish i can talk ferret but i cant i got him at PETCO where there were more of his kind i think they were all brothers and i think he misses them or maybe is something else i tried leave the cage open so now they can play around but he still cry's a little please help me because is making me so sad :-(