Dreaming of the letter X can mean that you are doing something that you should not be doing, or you are stopping yourself from doing something harmful. This can also mean a treasure, or it can mean something that will reward you for what you are doing.
Dreaming of getting an x-ray can mean that you are being tricked by someone that you know or that you need to look closer at a person that you know. This can also mean that you have a problem and you are working through it but if you have x-ray vision it can mean you are able to look at issues you are facing and solve them easily.
Playing a xylophone in your dream can mean that you are worried about the world around you or that you are wanting to be better attuned to your environment. This can also mean you are motivated to do things better and you want to have a happier life.