MY quiet line washing machine vibrates wildly and bumps around when spinnin?

This does not always happen, only sometimes & I think there is an earthquake, it jumps so violently. It was in the apartment to which I recently moved. I do not know how old it is, or the model number or how to locate this information. Usually it works very well, but something obviously needs to be fixed. I wonder if the drum is loose? It swings a little when I push it.