It means the hamster is scared or hurt. It is best to put the hamster back in the cage and leave it alone when this happens. The hamster may bite and scratch because it thinks you are going to harm...
It usually means that they're happy. If they vibrate violently, then they're extremely frightened. Put them down immediately. If they continue to vibrate like this, then you may want to get them to a...
When two hamsters are fighting, the weaker hamster, or the hamster that is giving in, screeches. Also when a hamster is very scared, or very distressed, it will make a screeching noise.