Okay I think I'm stating the obvious but I'll write this any way....
The Toe rod system(?) center of diff mounting to the lower knuckle is a ball joint, well sort of as it uses the same mechanical principals. If you have ever manipulated a ball joint going bad you have felt that it's not smooth, rather it feels notchy as it is moved in the socket. If you drive the studs out of the Knuckle and manipulate them they will either feel smooth and tight or loose and notchy. If they are dry then you could also expect noise something akin to the noise that a shot A-arm bushing makes...that annoying squeaking as the arm actuates over bumps in the road. You didn't describe the noise, high pitched squeaking (rust related) or a bass sounding clunking ( eroded ball & socket with too much end play in the vertical plane ) or snapping sound?
If the boots are cracked then the lube will have all run out and the joint is N/G. It will have rusted, or eroded or both. Too bad we can't lube them up at intervals.
Okay that's my two cents on the situation....
Tom