HELP! I'm running out of ideas

Thanks, I inspected the uca brackets but couldn't see any cracks or rust (but I'll check again to make absolutely sure) I'll also check the idler arm connection.

What's the best way of doing that, should it be up in the air or at ride height for that? I guess I'll try to see if it moves when I put some pressure on it with a crowbar or something?

The shaking/knocking happens way before lock. With the new borgeson box I installed there is absolutely no play at all when I turn the wheel while driving or being stationary.