It was pouring by me yesterday and I stopped at a traffic light with the wiper set to either lo or hi. I then noticed the car was rocking left and right. Anyone else noticed it?
My 1850-lb Insight nearly tips over it rocks so hard when the wipers are going. Our heavy Clarity also rocks, but a lot less. Interestingly, I believe the Clarity has a separate motor for each wiper, so there's not as much reciprocating linkage, etc. as in more primitive cars that use only one wiper motor.
Vibration should be less than most cars. The wipers are symmetric, and balance the torque of each other. Maybe you can ask dealer to adjust them.
