I prefer a rooftop car carrier to a rear mount system. With the bike on the back of the car, someone could rear-end you in a parking lot and bend your frame. Or what would be a very minor fender-bender on the road could ruin your bike. Of course, with a roof rack, you have to watch out for low underpasses. I believe you can get front-end covers for bikes so they don't get bug-splattered on the roof. I wouldn't worry about vibration - if the bike can take being ridden on rough roads with you aboard, it can take the auto vibration.