R33 Rear Bushes

[MrMike]

I just bought myself a 95 33 gtst.....when i go over bumps there is a slight knock coming from the rear.....the shocks are still really stiff so i think it could be bushes......how do i tell if they are buggered. i'm an auto electrician so i know how to use a spanner (or a test light) but have no idea how to diagnose suspension problems.....is it a hard job to change the bushes and will i be able to order them from auto one...etc...

Mick