Nova

Hi everyone! Anyone in chch a mini expert? I own a 1976 Austin Mini. There is quite a loud knocking sound coming from what seems the rear of the car when driven. It occurs when travelling at speed and I take my foot off the throttle I have been told the axle crosses are shot and need replacing... (pretty sure axle crosses aren’t a thing?) Can someone elaborate on this? Any advice on how to do it and where to get parts??? Or should I drop it to a shop