Hi, I recently bought Aero Wiper arms from a local breakers and fitted them to my B6. I also bought new Aero blades from my local audi dealer. The wipers look so much better but were only silent for about 5 mins of driving in the rain, then thump everytime the blade changes direction ( I have thoroughly cleaned the windscreen to make sure there is no traffic film or build up causing it but it still continues. Its driving me mad, i have to either keep the wipers off or turn the music up. Any suggestions as to what could be wrong? Dodgy blades from the dealer maybe?