DarkMirror

So after fixing my front swaybar links I got paranoid and was checking my rear suspension components (everything seems solid) and noticed my driver side rear coilover splash shield/sleeve/cover thingy was loose and slides up and down. My right side one doesn't slide or move. I tried looking it up and didn't find much, is this cause for concern and how do I reattach it so it doesn't jostle around? Everyone once in a while I can faintly hear it knocking about randomly.