Xylophones are quirky instruments that for most are connected with childhood music classes.
Playing a xylophone in your dream might suggest that you should try something different.
Also, some xylophones are made from metal while other are made from wood, which may be important to your dream interpretation.
For example, the little metal xylophones are more childish and connected with fun, while the larger wooden xylophones are more connected with nature and spirituality.