Are you sure it's not the universal joint from the main shaft? My yokes were worn and it caused it to make a loud knocking sound when ever going over bumps. To test it, pull the shaft, not the steering wheel, up and down and see if it makes a noise.
I simply got a 2nd hand rack with universal joint attached from an old corolla at the wreckers... hmm can't remember what type of rolla it was, but the easiest way is to take your rack in with you and match one up.
