because the cleats bear metal on metal, they can squeak once per revolution. Bearings can wear out if water gets in, the cones come adrift, etc.
Spindles can feel gritty when turned if the bearing is bad (of course) but also becuase there is dirt between the spindle and sleeve, the sleeve seal is bad, or the sleeve is deformed.
BTW if the cone and locknut come adrift (eg because they were never tightened properly), precession can cause the RH bearing to run loose and the LH bearing to destroy itself.
cheers