Just like you, your dog dreams when they sleep, and sometimes they make noises like whimpering in their dreams.
They might be dreaming about things that happened during the day, like playing with you or chasing squirrels.
Sometimes they might whimper if they are feeling stressed, haven't slept enough, or if they have a little bit of pain.
If your dog whimpers a lot, it's good to talk to the vet to make sure everything is okay.