Just like humans beagles can get very cold. I predict that your beagle is just a little chilly. Don't worry this is a normal behavior.
I heard Cesar Millan said that dogs are shaking when their head is thinking about doing a certain behavior but they are holding themselve from doing it. It is a transitional phase during training. After the release of this energy inside of them, your dog should stop shaking.
it's is common in dogs if they are young or they are nervous around something such as a certain individual.