the wheel starts to shake and makes a loud noice that almost sounds like thumping under my jeep whenever i turn the wheel more than a slight bit. is this the power steering pump goin out or just in need of more fluid? its a 99 cherokee sport straight 6 engine 4.0L any ideas?

Lift the front end of your Jeep off the ground, grab the wheel from the 12 and 6 o'clock and try to move it, if it clunks, your unit bearings are shot, cheap and easy fix. Grab the wheel from the 9 and 3 o'clock position and shake it, if it moves or clunks, check your tie rods. Also depending on your mileage, changing your ball joints might not be a bad idea.