1hotsteppa

Hello every1 i have a 98 impreza sport and my passenger side rear drive shaft seems loos as in if i grab hold of it i can move it a good inch or 2 in and out of the rear dif but i have no leaking oil and it seems to be driving ok. it rattles when i go over bumps and is starting to worry me does anybody have any ideas what could be the problem
any help would be really apreciated
thanks in advance