I wanted to put this here in case anyone else is stumped like me. I had a metal on metal clanking sound come from the back of my truck especially when rocking side to side. My son sat in the rear and pointed to the jack area. At first look i couldn't figure it out, but eventually i found that the bottle jack housing has a sort of rubber band hanging from the right side with a metal hook on the end. I am guessing that it's meant to secure the jack in the holder? Once I shook that hook it sure made the same sound when hitting the inside of the rear bodywork.