Sounds like the may have swarmed, or otherwise requeening. If you wanted to make sure they do well you might consider transferring a frame of eggs/brood from the stronger hive to the weaker.
Are you serious? Of course it is not going to sound the same. It only has a fraction of the bees. How much can 5000 roar?if you want to know if you have a queen in there just put your ear to the box and compare to the other hive that is doing well. if there is no queen the hive will be roaring/humming. Other wise i agree with the above posts, if you need a queen add a frame from the other with as young of brood as possible.