Noisy windscreen wipers on a 2016 Mini Cooper

I'm hoping you can assist me with an ongoing issue I've been having with my windscreen wipers on a 2016 Mini Cooper JCW.

I purchased the car in July last year as a 'dealer used' car, however it still has the new car warranty in place until December 2018. For the last six months I've been having issues with the windscreen wipers rubbing/bouncing along the windscreen when in use.

This has become a very frustrating issue and I've have not been able to revolve it. I first tried swapping the rubber wiper blade inserts but this was unsuccessful in fixing it. I then had the car checked at the Mini dealership in December 2017, however they only gave the windscreen and blades a good clean, and the issue continued. Then on April 4, 2018 I took my car back to the dealer again, this time showing them footage of the issue. They informed me that they had "readjusted the arms and cleaned the windscreen" and that everything was "ok".

However, the issue continues to persist. When the windscreen washer fluid is squirted onto the windscreen it reduces the rubbing and noise for a number of minutes until it starts again, it's when just plain water is on the windscreen that the issue is most obvious. I'm really hoping you can provide me with some guidance on how to resolve this issue, as the dealership appears incapable of fixing the issue. In my frustration with the dealership I'm considering taking the car to a local mechanic that worked on my previously owned car and seeing if he can fix the issue.

Even though I've still got the new car warranty until December 2018.