I have a new 2010 Mazda 3 Hatchback. When I’m driving and I lower the rear windows I get a thumping sound of air. I can feel it at speeds as low as 30 and the faster I go the stronger it get If I’m going 65 or 70 mph. the car vibrates so much that I can’t see out of the rearview mirrow. Is this normal for this car?

This is a common phenomenon on modern cars that are designed for driving with the windows closed and the A/C in operation. Some are worse than others, so I suppose that the Mazda 3 is worse than average in this respect. The drive for maximum aerodynamic effect has added to this effect.

Many cars today are designed to be driven with the windows closed. Cars are designed to be aerodynamic and have the least amount of wind resistance. Lowering the rear window while driving upsets the air flow around the car. I don’t think there is any problem with your car. What is interesting is that many cars give better mileage at highway speeds with the windows up and the air conditioning on than if the cars had the windows down and the air conditioning off.