if you park the car on level ground look at it from behind the wheels will be at a slight angle top going in.
or you can jack the car up by the body so the wheel is about 25mm off the ground put a bar/tyre lever under the wheel try to lift/rock the wheel if there is play in the radius arm the bushes have gone.
if you can get under the car whilst jacked up with wheel off the ground put a bar/tyre lever between the part of the radius arm with the bush in it and the body(under the car)and pull down if there is movment your radius arm bushes have gone.
But you should have heard a knocking noise from the rear anyway.
If you not got it ask again will try to put it a better way if you want me to hope this helps ....
RiB