nikosan

My front end will swerve occasionally while I am steering to the left. It will almost happen when I hit a freeway joist, a dip on the road. I took it to a reputable alignment shop to check my suspension components and he found it all intact and in good condition after doing an alignment. While I am making a turn to the left, my steering will swerve to the right at times. Could this be my rack and pinion failing? thanks for any advice