Rear end
Assuming anything on a, hmmmm, what type of car are we even talking about, is nutty. Is this an A body, a tractor or a ford? If so, it’s at least 48 years old or even 60+ years old. Over multiple decades, unless it’s been in your possession since new, it could have anything in there now. You gotta give us some facts/details before we can make useful suggestions.