klho

Don't know if it's the proper term but recently my new 1.8T wipers on the driver's side has been doing a little shudder i.e. not moving smoothly across the windshield but "skipping" over some spots. Nothing on a windshield nor the blades though. Brought in to dealer and initially they thought I had applied something on the screen e.g. RainX, but I really didn't and I've only had the car for 5 months. In any case they tried changing the blade and then the wiper arm but the shudder is still there. Btw I have the aero wipers so it should be even better that the older ones. Then they tried cleaning the windshield and it has improved, but still shudders at times.
Anyone has any experience with this? It almost seems like I have to apply something like RainX to get rid of this problem? TIA.