a knocking noise? to say the least. I had it in 6 months ago for a popping noise in fact I posted about it a week ago because its to the point that the dealership checked it over and found nothing wrong and I just happen to see this glob of grease as I walked by today. I hope this is the popping noise that I have been hearing. I am just glad that I actually have something to show them. The other side is cracking (the rubber boot) I am assuming that one is on its way out as well?
If the boot is just cracking, then you can replace it before the ball-joint itself drys out and goes bad. That's a relatively cheap/easy fix. If you already have a bad ball-joint, then you need to replace it and follow that up with an alignment...
You can check the ball-joints yourself by jacking up the car and wiggling the tire up/down and left/right with all your strength. If you hear any noises or feel looseness, have a friend wiggle the tire while you hunt around for problems. Be aware that some knocking in the steering column is normal due to the gears and moving components.
I had a cracked boot on my passenger ball joint. It still had grease but some leaked out. I can tell it's a little looser than the drivers side but isnt to the point of making noise. When I did my bushings I replaced my boots and repacked them with grease. Should be good for a while now. I'm going to get in the habit of checking them more often. Because the boot is a $3 part and will save you about $150 for a new knuckle because the ball joint can't be pressed in.
You can tell by turning the steering wheel left-right and the steering linkage & other steering components will move. Sway br end links are connected from the lower control arms to the solidly mounted sway bar. They don't move much, and really only when the wheels move up and down.