Steering Problem

Hello!
I have a '99 Grand Am 2.4L w/ 80,000 miles.
My problem is that when I pull out of a driveway, parking lot, etc. To the left it pulls to the left. Same thing if I pull out and turn right. It pulls to the right. Sometimes it is light, sometimes really hard (if you let go, you'd be in the ditch). I will tell you what I had done to it. I bought it used (private party) and it needed front tires, left front strut, and then I had it alligned. It was doing this "pull right/ pull left thing" from the start. Sometimes the steering would get tight and then "pop" and my mechanic said that was the steering rack. I had him put in a used rack for less that $100 for the part because I couldn't afford the $300+ a new one would cost. After that it started making a "clicking/ popping" noise while steering sometimes. You don't feel anything in the steering wheel like before though. I was looking on your site and the closest thing I see to my problem is "front strut upper bushings". Do you think this is the problem for the pulling one way then another? I'm lost and my mechanic doesn't really know. Would the steering rack cause this problem? Please give me an idea! Thanks!