This problem with windows down or sunroof opened is a result of air passing over that open hole with little turbulence. New cars are designed to disturb the air less which is good for MPG and low noise but is bad for windows/sunroof open motoring. The "clean" air moving past the opening is of lower pressure than the still air inside car so the air in car moves out which lowers pressure and then the pressure outside car is greater which moves air into car. You can see this leads to repetitive pressure rise and fall inside the car which is the fluttering noise with accompanying ear ache. The solution for sunroof-caused disturbances is to open the sunroof to a position approximately 2 inches short of full open. This solution is already in place on '96 and later 850's with their auto-open sunroof control. For window-caused disturbances there is no neat solution. You can do as others have suggested and open one of the front windows which relieves the pressure and minimizes or maybe completely eliminates the problem.