These are a couple of cool little devices that you can install inline with you washing machine water lines.  They basically absorb or prevent the clang or bang of a water hammer you may hear in your house when a water valve somewhere is turned off suddenly.  This was an issue for us for a lone time, we have a high efficiency washer and by its’ nature it cycles the water valve quickly to only let in small amounts of water. Thus, if we started a load before bed, we would hear the water hammer all the way upstairs basically coming from our master bath shower.  A plumber we had in for something else mention them when we were talking, and so I bought them from Home Depot and installed them. For about $11/ea, problem solved.