Oldsmobile/Buick Repair: 2001 buick Lasabre, cv joints, front end alignment

Question
I have a 2001 buick I am getting worried about driving because of the problems I think are dangerous and the dealer says they can find nothing.  At 65 - 70 miles an hour the car has a terrible vibration, it shakes badly.  The tires are very good.  It was put on the front end alignment machine and the dealer says it is not out of line.  Also, while turning a corner from a stop sign or from another street whether to the left or right I hear a definite 'klunk'  It causes the vehicle to pull to one side til I have to turn at another street and I get another klunk.  The dealer has had the car twice within the last 6 weeks.  The last time was for a whole week and still they say they cannot find the problem.  They 'said' it is not the struts, or the cv joints.  Help me, I am afraid since I think it affects the steering.    Thanks

Answer
Hello Barbara,
I am curious as to weather it actually pulls to one side after a turn, or is the steering wheel turned to one side.
It has rack and pinion steering, and I have seen the mounts for the steering assembly wear out, allowing the rack and pinion cylinder to shift to one side or the other.
See if they will check that.
It can be checked while sitting still. Have someone turn the steering wheel, while you watch the steering cylinder underneath the car, and see if it moves and pops.

Van