really random possibility that may be tied into the bar spread issue... but might they be 'too tight' that the metal lip thingy (that points up towards the bar on the inside of the clamp) is actually touching the bar, and thus, not really clamping down on the car? Just thought I'd throw that in as it has happened to me before- ended up actually loosening all around and retightening more evenly. another time I ended up remeasureing the mounting and that worked as well.
Also, random fun fact for anyone that may not have noticed..there are little bumps that, I think, are not so coincidentally placed at the exact point (centered I believe) right underneath where the feet are to go inside the doorframe/side of the roof. Barely noticeable, but a great guide if you take on and pull off the rack a lot and don't want to measure the gap distance, and keep your bars straight.