Washing machines by their nature will operate unbalanced; this is due to the clothes load being out of balance. A little vibration is to be expected. One thing to check, and I found it on our machine, is that the leveling screws, if any, are locked down. The leveling screws will be supporting the machine and they should have lock nuts which keep the leveling screws, they are like bolts with rubber pads at the bottom. The lock nuts will keep the leveling screws from loosening due to the vibration of the machine and if that happens the machine will shake and shudder ant you will think it is going to break. Get to a point where you can see the leveling screws (bolts) and look for a nut on the top of bottom of the screw. This bolt should be tightened against the frame of the washer. If it is not, you will see it is loose. Get a level and level the machine using the 4 leveling screws. Then tighten the lock nuts against the machine base and that should fix the problem.