Why is my hamster making weird noises while he is asleep ?

well my hamster is quite old but in the day when hes asleep he always makes these funny squeaking and like tummy rumble noises its really weird just asking if any ones hamster out there makes these noises hehe its kinda funny really but i am just wondering he is an old hamster and hes been doing it nearly all his life soooooooo yer thanks :)