Have you walked into your laundry room because your washer was on its spin cycle and creating a ton of noise? Did the washer vibrate so hard it appeared to be moving? This is an incredibly common problem with washers over time. What is happening is that your washer has fallen out of balance. When this happens, the force of the spin cycle can cause it to vibrate excessively. Sometimes it vibrates so excessively that it can actually move out of place. If your washer is out of balance, it may not always mean a problem, however.
Before jumping into an actual malfunction that is causing a washer to be unbalanced, it is best to consider the load you are washing. Different types of clothing, when wet, have different weights. This means that a mixed load has the potential to throw a washing machine off the balance if it has too much heavy weighted clothing, like jeans, settle to one side. Sometimes the solution to this problem is as simple as opening up your washer and redistributing the clothing or removing some items for a separate load.
If it is not the clothing causing the washer to be out of balance, then it is most likely the washer legs. All washers come with adjustable legs to account for uneven flooring. However, because they can move does mean that they can vibrate themselves out of adjustment.
With the help of a level, you should be able to deduce which leg has fallen out of level. The good news is that leg is actually really simple to adjust. Moving the leg is as simple as turning a nut on the leg until your washer reads level on all sides.
If you had a water leak recently in the area, it is also possible that your floor has warped. This can be a separate issue, but the fix for the washer remains the same since those legs were designed to compensate for uneven flooring.