They will develop a bit of slack in the spring loaded bushing that holds the rack against the pinion, which gives you a bit of a rattle through the steering column. Unfortunatly, the only way to buy the bushing and shims you need is to buy a complete overhaul kit, which is worth more than a rebuilt rack. On the plus side, it is only irritating- no danger of anything coming apart.

I presume you have checked bushings and mounting bolts and steering shaft joints et al.