knocking,rear diff noise?
 

hi there,i have a knocking,rumbling noise from the rear of my 95wrx,i have jacked the car up and checked every bush,drop link etc and there is no play in the wheels to indicate wheel bearing failure,however the rear diff is leaking pretty badly from the cover,i have not fixed this yet or checked the diff oil level,could this be the noise im hearing?it sounds more like a rear strut that is knocking,but again they look and work fine with no leaks. any help more than welcome thanks bryan