I work at the plant that manufactures the rack and pinion for Ford Rangers. Are you sure the sound is coming from the rack? As far as internal leakage goes, if you had internal leakage, it would feel as though you didn't have hydraulic assist. If the sound is coming from the rack area, then I would suggest looking at the tie rods, ball joints, or other steering linkage. If the sound is coming from the engine compartment, you may have a power steering pump going bad. Anyway, I hope this info helps.