The washer pounds out a syncopated beat you could dance to.
If you're not overloading the machine or creating unbalanced loads (mixing sheets and towels, for instance), check for level and adjust the feet as necessary. If that doesn't fix the problem, put your washer on antivibration pads (such as those made by Derens, available at homedepot.com
) to keep it from moving across the floor. If the machine is in a cabinet, apply stick-on rubber bumpers to the inside walls where the machine bumps it, to muffle the impact.