power steering hum

i have recently rebuilt the engine to my friends eclipse he just bought and everything went great till we drove it. the first time it got out, the steering was fighting us and making horrible hum/scratching noise. i figured it was probably air in the line or the belt was on too tight, since it has an underdrive pulley and the belt suggested for it was too tight. so we get back and loosen the tension and still its there. he said it was fighting him on the highway just bouncing all over the place at 65 mph but when i drove it back it was fine. also ball joints and tie rods are brand new, same with most of the suspension and cv joints.

This might be a stupid question but did you check the power steering fluid? I had a similiar problem and it was just low on power steering fluid.

yeah its full.