When i back up every now and then something from the rear of my car makes a clanking noise whats some posibilities i need to look for?

 

did you change the oil in the rear by chance, you have to make sure its the right stuff, becuase if its to thin, and the wrong weight, it will do that, it happened, to me i used mobil 1 syn, and it was to thin, and when i back up at certain times it did noise to, hope this helps, or it might be low to.