HELP! 1999 Chevy Blazer Power Steering Problem

1999 Chevy Blazer 6 cyl 130000 miles

At idle with the wheels straight.. my steering wheel vibrates slightly...as soon as i turn the steering wheel the vibration gets worse... i took the belt off the power steering pump pulley ..and started the car... i didn't feel or hear any vibration...even when i turned the steering wheel.

the fluid seems ok..
the belt and tension seem ok..
the power steering pump pulley doesnt seem to wobble at all...

i also hear what appears to be a knocking sound coming from the line that exits the power steering pump... that line is connected to the steering gear..the vibration/noise is felt more when i grab the line exiting the pump and less where it enters the steering gear.

the link below is an actual video i posted on youtube..you can clearly hear the knocking sound as i turn the wheel

http://www.youtube.com/watch?v=qdvzwmjQLq8&feature=player_embedded