Suspension needs replacing - noob question....
 

I'm starting to get some knocking from the rear end when going over pot holes. Car is 9 years old and 97k miles, so it's bound to be going wrong in places now.

I've also noticed that the suspension in general is getting a bit tired.

Am I right in thinking that the shocks are causing the knocking and the springs are making it feel tired?

Best changing both or just replace the springs (cheaper) and can you do anything to fix the knocking apart from replacing?

Is a coilover just a one peice shock/spring unit? I assume changing all four corners is best? (same front and back?)

Cheers
Richard.